Peggy and 
                                                    investigate the 
                                                    "murder" of a 
                                                    loyal Newton's 
                                                    Apple viewer.


How do forensic scientists help solve murders?


Whenever a person is murdered, the police initiate a thorough investigation into the crime, crime scene and friends and family of the victim. Each aspect of the investigation is important, but often it is the physical evidence of the crime that catches and convicts the criminal.

Criminal investigations involve a variety of scientific fields and complex instrumentation. Chemistry, physics and biology are used in combination when detectives and laboratory technicians investigate a murder. Special tests include determining blood alcohol levels, using chemicals to make almost invisible blood stains very visible and typing blood to identify possible suspects. Geometry and trigonometry help the investigators evaluate critical evidence like the angles of lethal blows and the trajectory of bullets. The tools of criminal investigations include computers, sophisticated photographic equipment, lasers, microscopes and other scientific equipment.

The study of both forensics and criminology require excellent observation skills and objectivity. The first official who arrives at the crime scene works quickly to seal off the area and preserve the scene as much as possible. Usually no one enters until the field investigator has had a chance to look about and collect every piece of evidence like hair and fiber samples, pieces of clothing or other personal belongings. Only then do other police officers or medical personnel enter the area.

When a piece of evidence is found at the scene of the crime, investigators are always careful to keep it in a labeled and sealed package until it can be safely stored in the police vault. It is only opened again when the case goes to court. This kind of evidence care-taking is especially important in drug-related cases when drugs are seized. Regardless, it is against the law to tamper with any kind of evidence.

Things to Talk About

  1. What examples of forensic science have you seen in television mysteries or movies?
  2. Would you like to be a forensic scientist? Why or why not?
  3. Is there such a thing as a perfect crime?

Criminology--The scientific study of crime as a social phenomenon.

Forensic--A science that deals with the relation and application of facts to legal problems.

Plaster of Paris--A white powdery substance that swells when mixed with water and sets rapidly; used in making casts and molds.

Serology--The scientific study of the properties and action of the chemistry of the blood.

Trajectory--The path of a flying object (or substance), which can be analyzed using basic laws of physics.


Additional Sources of Information

Activity Page

Step Right In!

Learn how you can capture foot prints and simulate your own criminal investigation.

Main Activity

Scene investigators are always on the lookout for finger and foot prints. These clues can be essential in identifying or eliminating murder suspects.


1. Divide your class into investigation and criminal teams. Have the "criminals" go outside and make footprints in some soft soil. Have some people wear their shoes and have others take them off.

2. While the "criminal" team is outside, the "investigation" team should mix the Plaster of Paris with water. Try to keep the consistency thick so that the impressions can retain small details.

3. The "investigators" should then locate the "criminals" footprints and spray each with the hair spray. This will keep the soil in place when you begin to make your mold.

4. Pour the Plaster of Paris into the prepared footprints. Pour slowly from the sides and be careful not to disturb the area.

5. Allow the mold to set.

6. Have the investigation team try to match the footprints to the correct member of the "criminal" team.


1. What types of soil would tend to make better prints?

2. Would an actual footprint or a print from a shoe or boot be more distinctive? Why?

3. What conditions could keep the footprints from showing up very well? What properties does hair spray have that makes it useful for shoe printing?

The orientation and placement of objects can be very important in criminal investigations. Learn about drawing to scale to make your own representative drawings. Measure your class room and any large pieces of furniture in the room. If one foot equals one half inch, how could you draw the room on graph paper. Ask someone to lay down in the room. Using their height and location can you draw them into your paper crime scene?

Collect a couple of pine cones or sea shells. Have several other people select one and study it for two minutes. Collect the pine cones or sea shells. Have everyone try to draw their particular object. Look at the group of items. Can you identify yours? After looking at someone else's drawing can you identify their item?

Have a person very quickly run into the classroom unexpectedly for about 10 seconds. They should be dressed in an unusual way. Write down everything you remember about the person including his/her size, hair color, clothing, or other details. Compare your list with other classmates. How many clues could you list? How could you improve your observation skills?

Practice fingerprinting by using an ink pad and white pieces of paper. Each finger should be rolled from side to side to make a good print. Be careful with the ink and your clothing. (If some of your friends do not want to take their fingerprints, be sure that you respect their privacy.) Compare everyone's fingerprints. What kind of differences do you see? Are there differences between your fingers' fingerprints?

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Educational materials developed with the National Science Teachers Association.

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