Teeth Impressions

Teeth and teeth impressions can be used in an investigation to identify an unknown person and to learn information about him or her. Try the following activity to learn more about what teeth can tell you.

Materials

- scissors
- Styrofoam plate
- Marking pen

Procedure

1. Cut the Styrofoam plate into six equal wedges.
2. Stack two of wedges together, and cut 1 inch (2.5 cm) from the pointed end of both. Throw away the pieces that you cut off.
3. Slip the cut ends of the two wedges into your mouth. Push them in as far as possible while still being comfortable.
4. Bite down on the wedges firmly, then remove them.
5. Label the top wedge Impression of the Top Teeth and the bottom wedge Impression of the Bottom Teeth.
6. Examine the teeth impressions. How many teeth made marks in the top impressions? How many made marks in the bottom impressions? What features of the impressions are useful in telling the top teeth from the bottom teeth? How are the teeth different?

More Fun Stuff to Do

Collect teeth impressions from several helpers. Be sure to label each impression with the person’s name whether it is the top or bottom teeth. Leave the room, then have one helper take a bite from a piece of cheese or hard chocolate. Can you identify who took the bite by comparing the impression in the cheese or chocolate to the set of impressions?

Explanation

Humans are provided with two sets of teeth, which appear at different times in life. The first set, called deciduous teeth, appear when we are children. The second and final set, the permanent teeth, appear later and replace the deciduous teeth.

This process of replacement begins at about age six, when we lose our front incisor teeth, and continues to about age eighteen, when we get our third set molars, commonly called our wisdom teeth. We have twenty deciduous teeth: four incisors and two canines (which cut or tear food) and four molars (which chew and grind food) in each jaw. We have thirty-two permanent teeth: four incisors, two canines, four premolars, and six in each jaw.
The arrangement of each person’s teeth is unique and can be easily used to help identify a person. The number and type of teeth are valuable in determining the age of the individual. Forensic dentists can compare teeth impressions to dental records. Eighty percent of time, teeth impressions are used to identify unknown victims.

Detective Science in Action

Teeth impressions have used to identify many criminals. One hungry burglar was caught because of a half-eaten piece of cheese he left at the scene of the crime. The burglar became hungry during a break-in and took a piece of cheese out of the refrigerator. He had just taken one bite from the cheese when he heard a noise. Startled, be dropped the cheese and ran out of the house. When police arrived, they found the cheese. They matched the teeth impressions of the suspect to the bite marks in the cheese.

Ballistics

A gun leaves an impression on the bullets that are shot from it. Forensic scientists can use these impressions to match bullets to the type of gun used. The field of science that studies bullets and other shot objects is called ballistics. Try the following activity to investigate how detectives can solve a crime by using their knowledge of ballistics to match bullets to a gun.

Materials
Ballistic evidence shown in the drawing

Procedure

1. Using the ballistic evidence shown, match the bullet found at the scene of a bank robbery with the sample bullets fired from several guns.
2. Which type of gun was used in the crime?

Explanation

The first thing that a forensic scientist will determine when examining a bullet is its caliber. A bullet’s caliber is the same as its diameter, the length of a straight line through the center of the flat end of the bullet. The diameter of a bullet is measured in either inches or millimeters. A bullet that is 0.22 inches in diameter is a .22-caliber bullet. It is used in .22-caliber rifle, which has a barrel 0.22 inches in diameter. Similarly, a 9-mm pistol uses a bullet that is 9 millimeters in diameter. Forensic scientists will compare the caliber of a bullet found at the scene of a crime to the caliber of a gun found on a suspect. But that is just the beginning of their ballistic analysis.

As early as the sixteenth century, gunsmiths were improving the speed and accuracy of guns by cutting grooves called rifling grooves around the insides of guns barrels. These grooves make the bullet spin down the barrel and in the air, thus increasing the speed and force of the bullet. Bullets are made slightly larger than the gun barrel to ensure a tight fit, which results in the characteristic rifling marks on the bullet after it has been fired.

Inside the gun barrel, the rifling grooves and the lands (the area inside the gun barrel that remains after the barrel has been grooved) create a distinctive pattern that does not change, so any bullet that passes through the barrel of a particular gun will bear the rifling marks of the gun. In addition to rifling marks made on the bullet, identifying marks are made on the cartridge (the cylindrical container of the bullet, which holds the gunpowder and stays in the gun when it is fired). These marks are caused by the firing pin (the piece of metal that strikes the cartridge and ignites the gunpowder).

Matching bullets to guns is one of the simplest procedures in forensic science. By the knowing the caliber of a bullet and the land and groove configuration, a forensic scientist can tell detectives what type of gun the bullet came from.

Detective Science in Action

Forensic evidence proves a person’s innocence as often as it proves a person’s guilt. Recently, for example, a prospector in Alaska was found in his remote cabin dead from a gunshot wound. The immediate suspect was the prospector’s partner. Indeed, when the police found the partner, he was carrying a recently fired rifle and had blood on his boots.

A hundred years ago, the partner would have been found guilty based on those two bits of evidence alone. But forensic evidence showed that the bullet that killed the prospector came from a pistol, not the partner’s rifle, and that the blood on the partner’s boots came from a recently killed deer.

Glass Fragments

Glass fragments are one the most frequently found substances at crime scenes: Criminals break windows to gain entry into buildings, hit-and-run accidents result in broken glass, and so on. Try the following activity to see how forensic scientists analyze glass fragments at a crime lab.

Materials

- jigsaw puzzle

CAUTION: Do not try this activity with actual glass fragments.

Procedure

1. Dump the jigsaw puzzle pieces onto a table or floor. Turn each piece facedown.
2. Assemble the puzzle using only the shape of the pieces as a clue, not the elements of the picture.
3. Did you find this easier or more difficult than usual?

Explanation

Forensic scientists at a crime lab use a technique called the jigsaw method to analyze glass fragments. The jigsaw method works because when glass breaks, its surface fractures unevenly. This breaking process produces unique shapes of glass that will lock only into the pieces that were next to them at the point when the glass broke, just as each piece of a jigsaw puzzle will lock only into the pieces that go next to it.

Forensic scientists use the jigsaw method of glass-fragment analysis to solve crimes. For example, investigators may wants to know whether a piece of glass found in a hit-and –run victim’s clothing matches the glass from a broken headlight of a suspect’s automobile.

As you saw in this activity, the jigsaw method is very difficult. Forensic scientists perform other tests to match glass fragments to the scene of a crime.

Tool Impressions

The soda machine at your school has been broken into and the money has been taken. Hall monitors stops two students from another school in the hallway and fined a crowbar in one student’s backpack. How can your school prove that these students committed the crime? Try the following activity to investigate how detectives can match tools to the scene of a crime.

Materials

- hammer
- 16d nail (about 3 inches [7.5 cm] long)
- scrap piece of plywood
- pliers
- crowbar
- screwdriver
- timer
- adult helper

Procedure

NOTE: This activity requires adult help.

1. Have your adult helper use the hammer to pound the nail into the plywood so that ½ inch (1.25 cm) of the tip of the nail sticks out the back of the wood.
2. Leave the hammer, pliers, crowbar, and screwdriver near the plywood.
3. Tell your helper that he or she will have 3 minutes to remove the nail from the board, using several of the tools that are supplied.
4. Leave the room and time your helper for 3 minutes while he or she performs the task. Do not watch while your helper removes the nail.
5. When 3 minutes are up, try to match the marks made on the wood with the tools that were used. Which ones are easy to match? How could police use this information to investigate crimes?

Explanation

Almost any device used to perform work can be called a tool, and almost every tool will leave behind some mark of its use. There are three categories of tool marks: impression, such as those made by a hammer or a crowbar in a soft surface; cut marks, such as those made by wire cutters, saws, and the like on material; and scratch marks, such as those made by a knife blade scraping over a surface. Like other forms of trace about which tools were used at a crime scene. If the tools found on a suspect match the tool marks left at the scene of a crime, police have evidence to link the suspect to the crime.

One of the most frequently found tool impressions is the ‘jimmy’ mark found at the site of a break-in or forced entry. These marks occur when a criminal wedges a jimmy--a crowbar, screwdriver, or tire iron--between a door and its jamb, or between a window and its still, and exerts pressure until the door or window opens. The hard metal of the tool compresses the wood, leaving an impression of the tool in the wood.

Casts

Footprints, shoe prints, and tire tracks found at the scene of a crime can be important evidence to connect a suspect with a crime. A forensic scientist makes a cast (a form made by pouring plaster of Paris into a mold) of this type of impression. Try the following activity and learn how to make a cast of a shoe print.

Materials

- tape
- 2 pieces of 1-by-10-inch (2.5-by25-cm) cardboard
- 2 pieces of 1-by-5-inch (2.5-by-12.5-cm) cardboard
- petroleum jelly
- shoes
- soft soil in an outdoor area
- plaster of Paris
- water
- paper cup
- craft stick
- timer
- newspaper
- small paintbrush

Procedure

NOTE: This is an outdoor activity

1. Tape the four pieces of cardboard together to make a 5-by-10-inch (12.5-by-25-cm) rectangular frame. Grease the inside of the cardboard frame with petroleum jelly.
2. Wearing the shoes, press the sole of one show into soft soil so that you leave a shoe print in the soil.
3. Surround the shoe print with the cardboard frame.
4. Mix plaster of Paris with water in the paper cup according to the instructions on the box of plaster. Stir with the craft stick.
NOTE: Be sure to mix the plaster in throwaway container. Do not pour plaster down the sink, as it can clog the drain.
5. Pour the liquid plaster over the print. Allow it to dry for 1 hour.
6. Lift the plaster cast out of the ground. The soil will stick to the plaster. Bring the plaster cast indoors and place it on newspaper. Allow the plaster to dry overnight.
7. Brush the loose soil from the cast with the paintbrush.
8. Observe the cast. What can you tell about the shoe that made the print?

More Fun Stuff to Do

Make shoe-print casts of several helpers. Can you identify which shoes made each print? Make a cast of the track made by a tire in mud. What can you tell about the tire by looking at the cast?
Explanation

Casts of impressions, such as shoe prints, tire prints, or even bare footprints, taken at the scene of a crime can connect a person or vehicle with the crime.

When a shoe makes an impression in soft material, such as soil, it leaves behind a negative mold of itself, including any special marks or a logo or tread pattern, may be visible. By carefully filling the mold with the plaster of Paris, investigators can make an exact reproduction of surface of the sole of the shoe.

This reproduction is then sent to the crime lab where forensic scientists analyze it and compare it to known objects. For example, the pattern on the sole of a running shoe can be used to identify the brand of shoe, or the wear pattern may indicate that the wearer walks with a limp or drags one foot. Similar marking on a tire cast can tell forensic scientists what of tire made the mark, and may even tell what type of car the tire were on.

Paper Fibers

A detective investigating a crime looks for any material that might connect a suspect with the crime scene. A burned match found in an ashtray can provide evidence that links a suspect to the crime. Try the following activity to see how the paper fibers of a torn match can help forensic scientists solve a crime.

Materials

- 3 identical unused matchbooks
- magnifying lens
- paper
- pencil

Procedure

CAUTION: Do not light matches during this activity.
1. Tear match out of each matchbook.
2. Use the magnifying lens to examine the torn end of each match.
3. Draw a sketch of the torn end of each match. Do you see any special features that would help you link the match to the matchbook from which it was torn?
4. Use the magnifying lens to examine each matchbook. Carefully examine where each match was removed from the matchbook. Can you find any evidence on the matchbook that would help you link the torn match to it?

More Fun Stuff to Do

While you are out of the room, have a helper remove a match from each matchbook. Can you link each match to the matchbook from which it was torn?

Explanation

Paper is made of various wood fibers that have been pressed together. These are randomly arranged in the paper and can be of various lengths. When you tear paper, the fibers separate. Since no two pieces of paper have fibers that are identical in arrangement and length, all paper tears differently. Even if you tried, you could not make identical tears in two pieces of paper.

Matches in a matchbook are made of paper. The end of a paper match torn from a matchbook is distinctive and can be used to match it to the matchbook from which it was torn. If a match torn from a matchbook is found at a crime scene and can be linked to a matchbook found on a suspect, this evidence could prove that the suspect was at the scene of the crime.

Cloth Fibers

Like hair, cloth fibers are among the most common items left as trace evidence at a crime scene. Forensic scientists analyze, identify, and compare cloth fibers to place a suspect at a crime scene. For example, wool thread caught on a window frame at a crime scene may match the sweater found at a suspect’s house. Try the following activity to see how fibers can be used as evidence in an investigation.

Materials

- several different fabrics, including some with natural fibers, such as cotton and wool, and some with synthetic fibers, such as nylon or crayon
- transparent tape
- several sheets of white paper
- marking pen
- magnifying lens
- microscope (optional)
- pen and pencils
- notebook

NOTE: If you used old clothing, be sure to ask adult permission first, or ask at your local fabric store for fabric remnants.

Procedure

1. Pull fibers from several fabrics.
2. Tape each fiber to a separate sheet of white paper. With the marking pen, label the fiber according to which fabric it is from and how it was obtained.
3. Examine each fiber with the magnifying lens and microscope, if available. Record your observations in your notebook.

More Funs Stuff to Do

Ask a helper to pull a fiber from one of the fabrics without telling you which fabric it’s from. Using your labeled samples and magnifying lens or microscope, can you identify what the fiber is and which fabric it came from?

Explanation

There are four sources of fibers: animal, vegetable, mineral, and synthetic. The most common animal fibers are wool, cashmere, and silk. The most common vegetable fiber is cotton. Asbestos is the only mineral fiber. Synthetic fibers make up about 75 percent of all textile fibers in the United States and are the most common fiber investigated in the crime lab. There are over 1,000 different types of synthetic fiber, classified by their chemical composition, fiber shape and size, additives, and manufacturing process.

Like hair, fibers are important trace evidence. A forensic scientist use a vacuum cleaner to collect fibers, hairs, and dirt found at the scene of crime. These materials are then taken to the crime lab to be analyzed and compared to known samples. Investigators can link a suspect to the scene of a crime by matching fibers found at the scene of a crime to fibers found on a suspect or in a suspect’s vehicle or home.

Hair specimens

Hair left at a crime scene can be important evidence in a forensic investigation. A strand of hair can indicate the age, sex, and race of the person from which it came. Microscopic examination of hair found at a crime scene can confirm that a suspect was at a scene. Not all hair evidence has to be human hair, for example, cat hair found at the scene of a robbery may match the cat hair found on a suspect’s coat. Try the following activity to see how hair is used as evidence in an investigation.

Materials

- strand of hair from several people or animals
- transparent tape
- several sheets of white paper
- marking pen
- magnifying lens
- microscope (optional)
- pen or pencil
- notebook

Procedure

1. Obtain strands of hair from several people. You can take some from their hairbrushes, or cut or pull with permission, several hairs from each head. Include pet hairs in your investigation, if possible.
2. Tape each strand of hair to a sheet of white paper. With the marking pen, label the hair according to whose it is and how it was obtained.
3. Examine each hair with the magnifying lens and microscope, if available. Record your observations in your notebook.

More Fun Stuff to Do

Ask a helper to choose someone who already gave you a hair sample and obtain another strand of hair from that person. Using your labeled samples and magnifying lens or microscope can you identify this person after comparing all samples?

Explanation

The first step in any laboratory examination of hair evidence is for the crime lab to determine whether it is human hair. This is done by first comparing the hair to known human samples. The next step is to note the features of hair, such as its length, diameter, and color, including the distribution of color (hair may be lighter on one end) and any evidence of dyeing or bleaching.

Hair that has been pulled from the scalp-as opposed to hair that has been cut or broken off, or that has naturally fallen out-will often have tissue sticking to the root (the enlarged part of the strand of hair that grows below the surface of the skin). This tissue can be used to identify the owner of the hair through forensic techniques such as blood factor analysis and DNA testing.

Voice Prints

If investigators have a recording of voice, they can use voiceprints, just as they use fingerprints, to help identify the person on the recording. A voiceprint is a pattern of wavy lines and whorls produced by a recording of a person’s voice. Voiceprints are as unique as fingerprints. Try the following activity to simulate your voiceprint.

Materials

- glue
- ¼-by-¼ inch (6-by-6-mm) mirror
- speaker with connecting wire (a speaker and connecting wire from an old radio is easiest to use)
- cassette recorder
- wire cutters
- flashlight
- cassette recording of your voice
- adult helper

Procedure

1. Glue the mirror to the speaker, about halfway between the center and the edge of the speaker.
2. Ask your adult helper to connect the speaker to the cassette recorder. This can usually be done by using wire cutters to remove ½ inch (1 cm) of insulation from the free end of the speaker connection on the back of the cassette recorder.
3. Darken the room, and then shine the flashlight onto the mirror. Note where the light reflects off the mirror and shines on the opposite wall.
4. Turn on the cassette recorder and play the tape. What happens to the light’s reflection on the wall?

Explanation

Voiceprints can used to identify a recorded voice. In this activity, the recorded voice creates vibrations that are sent to the speaker. These vibrations are unique to the voice and to the words that are being said. The vibrations cause the speaker and the mirror attached to it to move, which causes the light reflected off the mirror to move in the same direction. If you could mark the path that reflected light traced, you would have a line that similar to a voiceprint. It would be possible to identify who, or what, made the sound.

Forensic scientists use voiceprints to compare recorded voices. They normally have a suspect record a 2 ½ -second speech that uses then ten most common words: a, and, I, is, it, on, the, to, we, and you. They then compare the voiceprint used as evidence in a crime.

Detective Science in Action
The first application of voiceprints occurred in Connecticut, where a voiceprint was used to prove the innocence of suspect. The suspect was a man accused of using a telephone to make threats to a family. The principal victim claimed that the suspect had made the calls, while the suspect protested his innocence. Investigators made tape recordings of both the phone calls and the suspect’s voice. An analysis of the phone calls revealed that they had actually been made by two individuals disguising their voices. The suspect was released and the two guilty persons were arrested.

Tough Fingerprints

As you learned in Project Dusting Fingerprints, some surfaces are better than others for lifting fingerprints. On certain surfaces, even dusting will not make a latent print visible. However, forensic scientists have discovered new ways to make fingerprints visible on difficult surfaces. Try the following activity to learn how to collect tough fingerprints.

Materials

- jar with a lid or other closable container
- two 3-inch (7.5 cm) squares of aluminum foil
- super glue (or glue that contains cyanoacrylate)
- timer

Procedure

1. Open the jar and set it on its side.
2. Put extra oil on your fingertip by rubbing it alongside your nose or in your hair.
3. Press the oiled fingertip on one square of aluminum foil, and then put the foil in the jar.
4. Squeeze a small amount of Super Glue onto the other foil square. Put the second piece of foil next to the foil in the jar.
5. Close the lid of the jar and wait about 30 minutes.
6. Observe the first piece of aluminum foil, the one your finger touched. What do you see?
CAUTION: Be careful not to get the glue on your hands.

More Fun Stuff to Do

Try this procedure with other materials. Repeat the experiment, substituting the aluminum foil with squares of cardboard, wood, cloth, and other materials that did not work very well in Project Dusting Finger Prints.

Explanation

A fingerprint made on aluminum foil cannot be detected using normal procedures, such as dusting, and has to be treated with chemicals. One such chemical is cyanoacrylate, a chemical used in Super Glue and similar products. In this activity, cyanoacrylate in the glue rises into the air. Trapped in the closed jar, this chemical sticks to the invisible oils in the fingerprint and hardens on them. As more cyanoacrylate particles harden on the fingerprint, it becomes visible and can then be easily identified.

There are other chemicals that can be used to make latent fingerprints visible on certain surfaces. Ninhydrin is a chemical that reacts with sweat and oils in the fingerprint to produce a purple image. It is ideal for lifting fingerprints from paper and some other porous surfaces, like bare wood and plaster. Iodine vapor can bring out fingerprints made on rough, absorbent, light-colored surfaces, such as paper and cloth. The iodine vapor reacts with the oil in the fingerprint and turns the fingerprint brown.

Detective Science in Action

Fingerprints first played a major role in solving a murder in 1902. Joseph Reibel was found dead in his apartment in Paris, France. The detective assigned to the case was Alphonse Bertillon, one of the first detectives to collect and record the physical characteristics of criminals, including their fingerprints. At the crime scene, Bertillon found broken glass from a cabinet and blood on the carpet. It was obvious the intruder had cut himself and unknowingly left behind fingerprints on several pieces of the glass. By comparing the fingerprints on the glass to those of several known criminals, Bertillon was able to match them to the fingerprints on the record card of Henri-Leon Scheffer, a convicted swindler. Scheffer was picked up by the police, and burdened with guilt and remorse, he confesses to crime.

Dusting Fingerprints

How can detectives identify fingerprints left at the scene of a crime? They must remove the prints and transport them back to the crime lab, where they can compare them to other fingerprints on file. One way to locate fingerprints is by a technique called dusting. The fingerprints are coated with powder, then lifted and taken to the lab for identification. Try the following activity to learn how to dust and lift fingerprints.

Materials

- drinking glass
- cocoa
- small paintbrush
- transparent tape
- 5 sheet of light-colored construction paper

Procedure

Note: You get a better fingerprint when more body oils are present. To do this, rub each finger alongside your nose or through your hair before making each fingerprint.

1. Press one finger at a time on the side of the drinking glass.
2. Sprinkle cocoa on the glass to coat the fingerprints.
3. Very gently brush the powdered area with the small paintbrush. When you’ve brushed off the loose powder, you should see the fingerprints.
4. Lift each print from the glass by placing the sticky side of a piece of transparent tape on the dusted finger print and then carefully lifting the tape from the glass. The dusted fingerprint should stick to the tape.
5. Place each piece of tape on a separate sheet of light-colored construction paper.

More Fun Stuff to Do

Try to use other surface to dust for fingerprints. Put fingerprints on a variety of surface, such as wood, cardboard, aluminum foil, smooth paper, rough surfaces with talcum powder and light surfaces with cocoa.

NOTE: Be careful to avoid breathing in the talcum powder, as it can irritate breathing passages. Place prints made with talcum powder on dark-colored construction paper and prints made with cocoa on light-colored construction paper. Which surfaces allow you to make fingerprints that can be identified using the dusting technique?

Explanation

If a criminal’s hands are covered with dirt, paint, or other substances, his or her fingerprints may be easily seen. These are called visible prints. Other prints may be harder to see and may need treatment with chemicals or dust to make them visible.
The best surface for dusting latent prints is one that is smooth, flat, and firm. Fingerprinting with powders does not work well on a surface that is rough or too flexible.

There are several powders that forensic scientists use to dust for latent fingerprints. Two common powders are (1) vegetable black, a fine carbon powder similar to the pencil scrapings that you used in Project Taking Fingerprints, and the choice for light-colored surfaces, and (2) aluminum powder, a fine white powder used on dark-colored surfaces. Forensic scientists use a fingerprinting powder that contrasts with the color of the surface on which the fingerprint is located. This makes the dusted fingerprints more visible and easier to photograph for evidence.

Forensic scientists also add other chemicals, such as lead, cadmium, copper, and mercury, to fingerprint powders to make them stick better to latent fingerprints. Fluorescent and phosphorescent chemicals can also be added to fingerprint powder to make dusted fingerprints glow in the dark.

Classifying Fingerprints

As you’ve probably learned in the previous activity, it is difficult to identify fingerprints. They are rather small and contain a lot of detail. To simplify their identification process, forensic scientists use a classification system. Try the following activity and learn to classify fingerprints.

Materials
- magnifying lens
- several sets of fingerprints, your own and those of helpers

Procedure
1. Use the magnifying lens to observe several sets of fingerprints. Do you notice characteristic that any of them share? Can you group the prints into categories to make the identification process easier?
2. Look at the common fingerprint patterns in the diagram. Notice that arch and the loop can have several forms and may bend to the right or the left.
3. Try to match the fingerprints that you have collected to one of the common patterns.

Explanation

There are several ways to classify fingerprints. In this activity, you have tried one of the easiest ways. More complex classification systems break down the common fingerprint pastern into smaller groups. For example, forensic scientists divided arches into plain arches (arches that are rounded) and tented arches (arches that are pointed). Loops can be either radial loops, which loop from the right, or ulnar loops, which loop from the left. Similarly, whorls are classes into several subdivisions.

Even more complex classification systems, such as the Henry System, have been developed to help compare fingerprints. The Henry System use a number system to classify the characteristics of a fingerprint as well as the type of finger and hand from which it came. Investigators match a fingerprint to a person by matching the print’s numbers to others prints with the same numbers, rather than by individually comparing a suspect’s fingerprint to every fingerprint on file.

Fingerprints used to be examined and classified by hand. This was a slow, time-consuming process. Now computers can scan a fingerprint and compare it to huge files that have been collected from many police agencies, such as the FBI. This system, called AFIS (Automatic Fingerprint Identification System), can do the work in a fraction of the time. For example, it takes AFIS only two minutes to complete a fingerprint comparison that used to take years to complete by hand.

There is one limitation to AFIS and all fingerprint identification methods. Although there are cover 250 million people in the United States, there are only about 10 million sets of fingerprints on file in AFIS. If a criminal’s fingerprints are not on file, the system does nor work.

Burned Documents

Even a notice that has been completely burned can be important evidence in a investigation. Try the following activity to restore and read a burned document.

Materials

- ballpoint pen
- sheet of white paper
- metal pie pen
- matches (to be used only by an adult)
- cookie sheet
- ½ cup (125 ml) glycerin (available from drufstore)
- 1 ½ cup (375 ml) tap water
- spray bottle
- adult helper

Procedure

Note: This activity requires adult help.
1. Write the message “Robbery set for 3:00 p.m. on Thursday” on the white paper.
2. Crumple the paper into the ball and place it in the middle of the pie pan.
3. Have your adult helper use the matches to set the paper on fire.
4. Allow the fire to burn out and cool down. When the burned paper is cool, carefully transfer it to the cookie sheet.
5. Observe the burned paper. Can you still see any of the writing on the paper?
6. Mix the glycerin with the water and place the mixture in the spray bottle.
7. Carefully spray the burned paper with the mixture until the paper is completely wet. Gently unfold the crumpled paper and flatten it on the cookie set. Use more spray if necessary.
8. Observe the pape. Can you now read any of the writing?

Explanation

A document may be burned either by accident or on purpose. Either way, handling a charred or burned document is one of the most difficult tasks a crime lab can face. The documents must be transferred to the crime lab with the utmost care and are often hand delivered in a cotton – or wool- lined box. Once the document is in the lab, the forensic scientist begins the careful process of reading it.

First, the forensic scientist must flatten the burned document without causing it fall apart. The glycerin – and – water solution used in the activity softened the burned paper so that you could flatten it. Forensic scientists used a similar procedure. They float burned sheets in a large tray containing a mixture of glycerin, alcohol, and a chemical called choral hydrate to soften the paper.

Once the document is flattened, the forensic scientist tries to read it. Most ballpoint pen inks contain a small amount of metal in the dyes. These metals are able to survive fire, so anything written with a ballpoint pen can be seen when the paper is flattened. The forensic scientist then photographs the document as evidence.

If the writing on the document is not easily visible, the forensic scientist will sometimes photograph the burned document with special film called infer red film. This film enhances the writing on the document and helps make it more visible.

Ink Identification

A ransom note is important evidence in a kidnapping investigation. If forensic investigators can identify the pen that wrote the note, they may be able to link the note to suspect. There are several ways to identify the type of pen used to write a ransom note or either criminal communication. Try the following activity to investigate one way to identify ink and the pen it came from.

Materials

- scissors
- coffee filters
- ruler
- water-soluble felt-tipped pens of different brands and different colors
- drinking glass
- tap water
- paper towel

Procedures

1. cut the coffee filters into several strips 1 inch (2.5 cm) wide.
2. Make a thick circle with one felt-tipped pen about 1 inch (2.5 cm) from the end of one strip.
3. Pour water into the drinking glass so that it fills ½ inch (1 cm) of the bottom of the glass.
4. Dip the end of the strip in the water so that the water covers about ½ inch (1 cm) of the end of the strip that you marked. The water should not touch the circle you drew.
5. Watch the water creep up the strip until it reaches the top of the strip.
6. Take the strip out of the water and place it on the paper towel. Above the filter, write the name of the color of the pen on the paper towel, using the same pen you used on the strip.
7. Repeat the experiment with the rest of the strips and pens.
8. Observe what happened to the circles made on the strips. What do you notice about the dyes in the pens?

More Fun Stuff to Do

Give a helper several different felt-tipped pens of the same color. Leave the room while your helper writes a short note, such as “Give me the money, or else!” on a coffee filter strip. Using the procedure you learned in the activity, can you tell which pen was used to write the note?

Explanation

Ink is complex chemical made up of several chemicals. Through a process called chromatography, complex chemicals like ink are separated into the chemicals of which they are made.

In this activity you performed an ink chromatography test. The colors of the inks separated in the different patterns because the ink colors are carried by the water at different speeds.

A forensic scientist can compare the chromatography pattern of the ink used to write a note with the chromatography patterns of several different known pens. This allows him or her to identify which pen was used to write the note.

Blood Identification

A few drops of a red substance are found at the house of a missing person. Are the drops red paint, ketchup from a hot dog, or possibly blood? The identification of the substance is important and will help a detective know which way to direct an investigation. Try the following activity to see one way that investigators determine the identity of a red substance.

Materials
- eyedropper
- red watercolor paint
- ketchup
- blood (from the bottom tray of a meat container)
- plate
- tap water
- Hemastix (available from many drugstores)

Caution: Be sure to wash your hands thoroughly after handling raw meat.

Procedure
1. Use the eyedropper to place 1 drop of red watercolor paint, 1 drop of ketchup, and 1 drop of blood on the plate.
2. Add a drop of water to ech red drop to make sure that they do not dry out.
3. Put a Hemastix strip in each solution. What happens? What color does the Hemastix strip turn in each solution? What color indicates blood?

Explanation

The Hemastix change color in blood. A Hemastix strip contains chemicals that will react with the chemicals normally found in blood. This simple test is often done at the scene of a crime as a quick way to determine whether a substance is blood. Later, Samples are tested in the laboratory to confirm the field test. Other tests, such as bloodtyping or DNA profiling, give more detailed information about the blood and the individual it came from

Mystery Substances

Any unknown substance found at a crime scene may be important evidence. The liquid left in a drinking glass might be a poison, or the residue found on a suspect’s hand may be gunpowder. As you know, forensic chemist perform many tests on unknown substances in order to identify them. Color, odor, and reaction to other substances are all clues to identify of an unknown substance. Try the following activity to perform another important tes.

Materials
- 1 ½ quarts (1.5 liters) tap water
- 2 quarts (2 liter) saucepan
- 2 red cabbage leaves
- timer
- colander
- plastic bowl
- marking pen
- masking tape
- 5 jar or glasses
- measuring cup
- 3 tablespoons (45 ml) concentrated lemon juice
- 3 tablespoons (45 ml) vinegar
- 3 tablespoons (45 ml) disitilled water
- 1 tablespoons (15 ml) baking soda
- 3 tablespoons (45 ml) ammonia
- pencil
- sheet of white paper
- adult helper

Proceduse
Note: This activity requires adults help.
1. Put the water in the saucepan. Tear the red cabbage leaves into small pieces and place them in the water.
2. Have your adult helper heat the water to boiling and boil the leaves for 5 minutes. Allow the liquid to cool.
3. Hold the colander over the bowl and have your adult helper carefully strain the leaves through the colander. Throw the leaves away.
4. Use the marking pen and masking tape to label jars from 1 to 5.
5. Pour about ½ cup (125 ml) of the cabbage juice into each jar.
6. Add the lemon juice to jar 1, the vinegar to jar 2, the distilled water to jar 3, the baking soda to jar 4, and the ammonia to jar 5.
7. Observe the color that each substance turns the cabbage juice, and record the the color on the chart similar to the one shown.

Caution: Be careful not spill the ammonia on your hands.

Jar Chemical Acid/Basic Colour
1 lemon juice acid
2 vinegar slightly acid
3 distilled water neutral
4 baking soda slightly basic
5 ammonia basic

More Fun Stuff to Do
Use the remaining cabbage juice, ½ cup (125 ml) at a time, to test various household substances. Set up new jars of cabbage juice, add the substances to the juice, and observe the color the juice becomes. Based on the color, use the chart to determine whether the substance is acid, slightly acid, neutral, slightly basic, or basic.

Explanation
There are many tests that forensic scientists perform on unknown substances. A forensic scientist will be first observe the unknown substance, gathering information about its physical characteristics, such as color, texture, Odor, melting point, and boiling point.

Next, the forensic scientist will test the chemical characteristics of the unknown substance. Certain substances are chemicals called acids or bases. Cabbage juice is a chemical indicator that changes color in the presence of an acid or a basie. If the substance tested is acid, the cabbage juice turns red. If the substance is basic, the juice turns green. Listed bellow are the expected results for this activity.

Jar Chemical Acid/Basic Color
1 lemon juice acid red
2 vinegar slightly acid pink
3 distilled water neutral dark purple
4 baking soda slightly basic light green
5 ammonia basic green

Litmus paper is another chemical indicator that can be used to test whether a substance is an acid or a base. You may have used litmus paper in school. The pH scale describes the strength of acid s or bases. Sensitive pH paper or pH meters tell not only whether the unknown substance is acid or basic, but also how strong the acid or basic is.

Taking Fingerprints

People have noticed the subtle differences in the fingerprint patterns for hundreds of years. Centuries ago, Chinese and Japanese emperors signed papers with thumbprints to make them authentic. But it wasn’t until the late 1800s that fingerprints were used as evidence to link a suspect to a crime. The first step in understanding fingerprints-and fingerprinting-is to examine your own.

Materials
- magnifying lens
- ink pad
- several sheets of white paper
- marking pen
- pencil
- transparent tape
- helper

Procedure
1. Look at your fingerptips through the magnifying lens and examine the patterns on your skin. These are your fingerprints. Can you describe them in words?
2. Make a set of your fingerprints. There are two easy ways to do this.

Method I
a. Press one finger at a time into the ink pad, being careful not to get your fingers too wet.
b. Have your helper make your fingerprints by holding your hand steady and pressing and rolling your fingers one at a time onto a clean sheet of white paper. Be careful not to smudge the prints.
c. Use the marking pen to label each print with the name of the finger from which it camel thumb, index finger, middle finger, ring finger, pinkie.

Methode II
a. Rub the pencil point back and forth many times on a clean sheet of white paper to make a small dark area of pencil-lead dust.
b. Press one finger at a time into the dust. You may need to rub the pencil point again to get more dust for each fingerprint.
c. Have your helper place the sticky side of a piece of transparent tape on each dusted finger.
d. Tape the prints to another clean sheet of white paper.
e. Use the marking pen to label each print with the name of the finger from which it came.

3. Examine both types of fingerprints with a magnifying lens.

More Fun Stuff to Do
Using either methode. Create a complete set of fingerprints for each of several helpers. Use one sheet of paper for each set, and label the prints so that you know which fingers and which person they came from. Next, have each helper make a fingerprint on separate sheet paper. Do not label these prints. Choose one of the sheets of paper at random. Using your labeled sets of fingerprints, try to figure out whose fingerprint it is. What can you do to make the task easier?

Ask an adult arrange a trip to your local police station to observe how the police take fingerprints. How do their methode compare to the two methods you learned?


Explanation

The skin on the palms of our hands (and the soles of our feet) is covered with tiny raised lines, called friction ridges. These ridges allow people to pick up and handle objects easily. Each person, even an identical twin, has a totally unique pattern of ridges on his or her hands and feet. And for each person, the pattern on each finger or toe is unique and different from the pattern on every other finger or toe.

A fingerprint is an impression of these ridge patterns transferred to a surface. Fingerprints occur because glands in our hands and feet secrete liquids, mainly sweat and oils. These liquids leave the patterned mark of our fingerprints on almost everything we touch.

There are three ways that fingerprints are valuable as evidence. First, fingerprints can confirm the identity of a person. When a criminal is taken into custody, it is a fairly simple task to take his or her fingerprints and cross-check them against other prints. This will prove who the criminal is and determine whether he or she has a criminal record or whether he or she is wanted by the police.

Second. Fingerprints can be used to compare a suspect in custody with fingerprints left at the scene of a crime.
Third, forensic scientist can compare fingerprints left at the scene of a crime with those of a known criminal whose fingerprints are on record.

Lip Prints

Women who wear lipstick often leave lip prints on drinking glasses. At a scene, this kind of print would be collected as evidence during an investigation. Try the following activity to learn how lip prints can be used to solve crimes.

Materials
- Lipstick (dark colors work best)
- White paper
- Pen or pencil

Procedure
1. Put lipstick on both of your lips. Rub your lips together to spread the lipstick evenly.
2. Fold the white paper in half.
3. Place the folded piece of paper between your lips and firmly press your lips against it. Be careful not to slide your lips on the paper or else the lip print will smudge.
4. Remove the paper and unfold it. Write your name on the paper to identify the lip print as yours.
5. Examine your lip print. What do you notice about it? Are there any unique qualities that would let you identify it as yours?

More Fun Stuff to Do
Collect lip prints from several helpers. Make sure that you write each person’s name next to his or her print. Then leave the room and have one of your helpers make a lip print on a drinking glass. Can you identify who made the print?

Explanation
There are many ways to identify a person. One of them is cheiloscopy, or the study of lip prints. (The term cheiloscopy comes from Greek word cheilos, meaning “lip”.) Lip prints are unique and do not change during a person’s life. Although they are less commonly encountered than fingerprints at the scene of crime, lip prints found on drinking glasses, cups, and even letters can be valuable evidence. One problem with lip prints is that their credibility has not yet been established in courts of law.

Mystery Powders

White powder found at a crime scene or in a suspect's pocket may be an illegal substance or merely sugar. A detective will have a crime lab identify the substance to determine whether a crime has been committed. Try the following activity to learn how forensic chemists use chemistry to identify unknown substances.

Materials
- Pencil
- Sheet of white paper
- measuring spoon set
- baking soda
- sugar
- salt
- cornstarch
- 4 sheets of black construction paper
- white chalk
- magnifying lens
- eyedropper
- water
- 4 small jars
- iodine solution (available at most drugstores)
- dish towel
- vinegar

Procedure
1. Use the pencil and white paper to create a chart similar to the one shown bellow.
2. Put 1/4 teaspoon (1 ml) of each white powder (baking soda, sugar, salt, and cornstarch) on a separate sheet of black construction paper. Use the chalk to label each powder.
3. Examine each powder with the magnifying lens. What does each powder look like? What its shape? Are its grains large or small? Record your observations in the appearance column of the chart.
4. Rub each powder between your fingers. How does it feel? Record your comments in the Texture column.
5. Do any of the powders have a smell? If so, record that information in the Smell column.
6. Use the eyedropper to place a drop af water on each powder. What happens? Do any of the powders dissolve or react in any other way? Record the results in the Reaction to Water column.
7. Put ½ teaspoon (2 ml) of each powder in a separate jar. Use the eye dropper to add 2 drops of iodine solution to each jar. Observer what happens and record your observations in the Reaction to Iodine column.
8. Rinse and dry the jars.
9. Put ½ teaspoon (2 ml) of each powder in a separate jar. Use the eye dropper to add 2 drops of vinegar solution to each jar. Observer what happens and record your observations in the Reaction to Vinegar column.

Appearance:Texture:Smell:Reaction to Water:Reaction to Iodine:Reaction to Vinegar
Baking Soda:
Sugar:
Salt:
Cornstarch:


More Fun Stuff to Do
Can you identify a mystery powder? Have a helper give you a small amount of one of the white powders without telling you which one it is. Repeat the chemical tests on the mystery powder and compare your results to those on the chart to identify the powder. Check with your helper to see whether you were correct.

Explanation
The results of your tests in this activity should be similar to those listed in the chart bellow.
If you did the More Fun Stuff to Do Activity, you should have been able to identify the unknown substance by repeating the tests and comparing your results to the results listed in your chart.
Just as you did in this activity, forensic scientists use a variety of tests to identify an unknown substance. Some tests examine the physical characteristics of a substance, such as its color, shape, and so forth. Other tests explore how it reacts to an acid, and so on. Forensic scientists compare the results of tests done on unknown substances to the results of tests done on known substances to identify the unknown substances.