Tailing a Suspect

Sometimes during an investigation, a detective has to tail, or follow, a suspect. The suspect may make contact with other suspects or might lead the detective to more evidence. Try the following activity at school or another safe location to test your ability to tail a person.

Materials

- Notebook
- Pen or pencil
- Watch
- Several helpers


Procedure
1. Gather several helpers together. Inform them that at some point during the next week, you are going to tail one of them as part of an experiment. (Telling them that you are going to tail them makes your task more difficult but will avoid their embarrassment.)
CAUTION: Tail the person at schol or in another safe location, such as a party. Never wander around alone.
2. Choose a day and select one person to follow for one hour. Use your notebook to record notes of his or her activities and any people the person encounters. Record the time for all notes you make.
3. When you have finished tailing the person, review your notes. Are there any activities that surprised you? Could you tell exactly what happened during each encounter with other people? Did the person figure out that you were tailing him or her?

More Fun Stuff to Do

Detectives seldom follow a suspect by themselves. They usually work in teams to prevent the suspect from getting suspicious. Often a second, third or even a fourth detective will pick up the trail where the previous detective leaves off. Try using a team to trail one of your helpers.

Explanation

It is difficult to tail a person without being noticed. If a suspect sees the same person, especially a stranger, over and over again, the suspect’s brain is alerted that something out of the ordinary has happened. He or she will become more cautious and will try to see whether someone is indeed tailing him or her. This is why the police use teams to follow suspects. One person will follow the suspect for a short time, then a second, third, or eve a fourth detective will pick up the trail. The suspect does not see the same person, so the suspect’s brain is not lerted that something unusual is happening.

Tailin a suspect is a form of surveillance. The term surveillance comes from the French word surveiller, which measn “to watch over.” Police practice surveillance for many reasons. They may watch a suspect’s home or place of work in order to gain information or even to catch the suspect. This is sometimes called a stakeout. They may trail a suspect to get other information, such as a suspect’s habits, daily routine, personal contacts, and place of work, home address, or type of information used.

The detective can be use the information gathered from observing a suspect to form a hypothesis or theory about the suspect, just as a scientist uses information to form a hyphotesis about an experiment. For example, if a suspect meets with the same person ath the same time every day and is seen passing slips of paper to that person, then the detective might make the hypothesis that the suspect is involve in a gambling operation and that the slips ofpaper are betting slips. The detective will then continue to investigate to determine whether that hypothesis is correct, in the same way that a scientist will test a hypothesis through experimentation.

Interviewing Witnesses

During an investigation, much of a detective’s time is spent interviewing witnesses and questioning suspects. If everyone tells the same story, a detective can feel confident that he or she has learned the truth about a crime. But often people lie, or they believe they are telling the truth but are mistaken. Try the following activity to see how good you are at interviewing witnesses.

Materials

- Copy of the picture on crime scene
- Watch or clock
- Pen or pencil
- Notebook
- Several helpers

Procedure

1. Have all of your helpers but one leave the room.
2. Give a copy of the picture on crime scene to the helper.
3. Using the watch or clock, give your helper 1 minute to look at the picture, than take the picture away.
4. Ask your helper what he or she remembers about the picture. Ask questions like “How many people were in the picture?” or ”Was there anything unusual that you noticed?” Record the answers in your notebook.
5. Repeat the procedure with each of the remaining helpers, making sure that the helpers do not hear each other’s answer to your questions.
6. Compare the comments that the helpers made. How many details were mentioned? Did some statements conflict with other statements?

More Fun Stuff to Do

Stage a pretend crime during a party or family gathering, and see wether any of the guests can figure out who did it. You could have someone “steal” some books off a shelf or remove a candlestick. At some point after the crime, choose several guests as witnesses and question each in a separated interview. How did their observations compare? Were their observations good enough for them to figure out who took the books?

Explanation

When interviewing witnesses to a crime, there are several questions that detectives ask to get a description of and information about the suspect. Some typical questions include: What is the sex, race, and approximate age of the suspect? What is his or her height, weight, color of hair and eyes, and complexion? Did you notice any physical scars or marks? Did the suspect wear glasses or have facial hair? What was the voice like? What was the suspect wearing? What did the suspect do?
Interviewers must listen for unexpected information. Often the question will cause the person who is being interviewd to implicate another person, meaning the person will reveal, by accident or on purpose, that someone else was involved in the crime.

Interviewers should remain impartial when they interview witnesses. This means they should not reveal their own opinions or feelings during the interview. Also must be careful not to lead a witness to say something that is not true.

Interviewing witnesses and other methods of crime detection are similar to scientific investigation in general. Scientist brings their own thougts and opinions to their experiments. Often they want an experiment to turn out a particular way, so it is difficult for them to remain impartial. This explains why two scientists, seeing the same information, can come to two opposite conclusions. Each bends the information to support his or her own views. Whether investigating crimes orperforming experiments, scientists must always keep an open mind and be ready for unexpected data.

The Scene of the Crime

It’s no exaggregation to say that following proper procedures during the first investigation of the crime scene can make the difference between a solved crime and an unsolved one. Try the following activity to learn some of the procedures performed at the scene of a crime.

Materials

- Your bedroom or another room of your house
- Several sheets ofwhite paper
- Marking pen
- Masking tape
- Pen and/or pencil
- Notebook
- Camera (optional)
- Tape measure
- Several plastic bags

Procedure

1. Pretend a crime has been commited in the room you’ve selected. Suppose something has been stolen from the room.
2. Secure the scene of the crime. With a sheet ofpaper and themarking pen, make a sign that reads, POLICE INVESTIGATION, DO NOT ENTER.Use the masking tape to tape the sign across the entrance to the room.
3. Begin to record your observations of the room in your notebokk. Remember, when investigating a crime scene, you cannot knowwaht is important and what isn’t. You need to record everything you find. If you have a camera, take severalpicture of the room.
4. Use another sheet of paper and the pencil to make a sketch of the room. Measure the dimensions of the room using the tape measure, and record the measurements in the sketch. Draw in window and door locations and the placement eny funiture.
5. Examine the roomcarefully. Record your observations in your notebook. Add to your room diagram the location ofany important items you find.
6. Begin to look for physical evidence may include hair and fibers, a glass or other object that could contain fingerprints, a diary or notebook, or anything else you think might be important. Examine the wastebasket. What do its contents tell you?
7. Save each piece of physical evidence in a plastic bag to examine later using the procedurs you’ll learn.

Explanation

The first duty at the crime scene is to secure the scene of the crime. This is usually done by the first police officer to arrive. If a person is badly injured at the scene, the officer will give assistance and call for medical aid.

Many crimes are investigated by the police officer on duty, but in more serious crimes, such as those that involve serious injury or the loss of expensive objects, a detective is often assigned to the case. A detective has usually received additional training, beyond that given to a police officer, in how to investigate a crime. When the detective arrives, he or she begins to record the scene of the crime by taking photographs, making sketches of the site, and taking notes.

The detective or members of a special forensic scinece team collect physical evidence. Physical evidence cololected from the scene of the crime is stored in labeled bags or containers, and then sent to the forensic science laboratory for later investigation.

The investigators at the crime scene must be very careful to collect and preserve allphysical evidence and to record all of their observatios. These data will be used later to solve the crime.

Detective Science in Action

You never know when something unusual found at the scene of a crime will be important to an investigation. In 1994 Dr. Gail Anderson, a forensic entomologist (a scientist who studies insects), was asked to aid wildlife enforcements officials who were trying yo put a stop to poaching (the killing of wildlife either without a license or out of season). In British Columbia, Canada, poachers often kill black bears and take their gallbladers, small internal organs that are valuable in certain cultures.

Investigators found insects on several black bears that had been killed by poachers. Dr.Anderson knew that insects have specific stages of development, from egg to adult. By examining the stage of the insect’s development and working backward, she was able to approximate the actual date the bears were killed. Wildlife officials could then focus their investigation on individuals who were in the area on that day. The insects found on the bear’s eventually led to the arrest of the poachers.

Mystery Box

Good observation skills involve all the scenes (the ability of the brain and nerves to react the world around us through sight, hearing, smell, touch, and taste). Sight is just one of the senses. What a forensic scientists, detective, or witness hears, smells, feels, or tastes may also be important clues. Try the following investigation to sharpen your nonvisual observationn skills.

Materials

- empty shoe box or similar box with lid
- various objects made from different materials-such as a rubber ball, a roll of toilet paper, a metal jar lid, a bar of soap, a plastic toy, a piece of fruit such as an apple, banana, or orange, etc—gathered by your helper with out your knowledge
- helper

Procedure

1. Leave the room.
2. Have your helper put several of objects in the shoe box and put the lid in place.
3. Return to the room and, without opening the box, try to guess how many objects are in the box and what the objects are made of. If possible, guess what the objects are. You can tilt, gently shake, and smell the box to help you.
4. After you have made your predictions, open the box and see how well you did. What objects were the easiest to determine? What objects were the hardest to determine?
5. Repeat the activity with other objects. Give your helper a turn at guessing.

More Fun Stuff to Do

To develop your sense of touch, have a helper first blind fold you and then put several objects in front of you. Touch the objects, but do not pick them up. Can you identify them? Without removing the blindfold, pick upthose that you could not identify. Can you tell what they are now? Remove the blindfold and see how well you did. Repeat the activity with other materials, but this time have your helper wear the blindfold.

Explanation

Forensic scientists and detective must use all five of their sense when investigating a crime. They often use the sense of sight to observe the scene of the crime and record what they see. But often the other four senses--hearing, smell, touch, and taste--will give a forensic scisntist information that may or may not be important evidence or clues. For example, that faint smell or bitter almond in a dringking glass might mean cyanide poisoning. Three loud bangs heard by witnesses could be gunfire or just a car misfiring.

Here is an exercisethat you can use to improve your other senses. Sit on a park bench on a warm spring day. Close your eyes and observe what is happening around you. Can you identify five sounds that you hear? Can you identify three smells?

You Are The Detective

Your mother picks you up from school one afternoon. Before returning home, she has to stop at the bank to make a deposit. The two of you stand in line at the bank, waiting for your mother to be helped. Suddenly, one of the tellers screams, “We hav been robbed!” What did you see while you were standin in line that might help with the investigation of the crime? Use your powers of observation to see what you remember.

Materials

- Picture on the stage
- Timer
- Pen or pencil
- Paper

Procedure

1. Observe picture on the stage for exactly 30 seconds. Look at everything that you thing might be important.
2. After 30 seconds, cover the picture and answer the question below. Write the answers on the sheet of paper.
3. How observant were you? Compare your answer to the picture.

Questions

1. What time was it on the clock?
2. What was the date?
3. Describe the person at the front of the line. Was it a man or a woman? Was he or she wearing a hat? What kind of clotes was the person wearing? Could you tell how tall the person was? Did he or she have any distinguishing features?
4. Did you notice anything unusual in the picture?

More Fun Stuff to Do

Repeat the activity, but this time put the picture away overnight and try answer the questions the next day. How good is your memory of the picture after 24 hours?

Explanation

When you observe, you create in your mind images of what you see. But what you see also has to be transmitted to your brain and stored in order for you to remember it later. As you found out in this activity, there is a lot of room for error in this process. When you first observed the picture, maybe you didn’t notice certain details. Or may be you saw details but didn’t think they were important to make a point of remembering them.

If you did More Fun Stuuf to Do activity, you also know that time affects memory. Much of what we observe is stored in our short-term memory, and we remember it only for a few hours, or may be only a few minutes.

If we store observations in our long-term memory, however we may remember them for years. Repeating something over and over help us remember it. Another helpful way to remember something is to associate it in our minds with something else. For example, most people would not be able to draw a map of Poland from memory. But if asked to draw a map of Italy, many people would be able to draw a fairly good sketch. Why? Because the shape of Italy resembles a boot. The shape of Italy sticks in our mind because we associate it with a common shape.

You can improve your powers of observation by doing the following exercise. Look at a department store display window for 30 seconds, then turn away and write down everything that you saw. Compare your notes with the real thing and write down the items that you left out. If you keep practicing this, your powers of observation will greatly improve.

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.