Forensic Evidence: Types, Definition & Cases

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  • 0:03 Hidden Evidence
  • 0:45 Science at Work
  • 1:11 Types of Forensic Evidence
  • 6:34 Lesson Summary
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Lesson Transcript
Instructor: Rachel Leintz

Rachel has taught in the fields of Forensic Science and Criminal Justice for over 7 years and has a master's degree in Forensic Science

The term 'forensic' actually means relating to law and science. In this lesson, we'll review different types of forensic evidence. We'll also look at real world cases where forensic evidence was used to solve crimes.

Hidden Evidence

It's 3 AM. You are on call for the Violent Crimes Response Unit. You arrive on the scene of a missing person case. No one has seen the home owner in about a week, and the Homicide Sergeant has asked you to examine the home for anything indicating that a crime may have occurred. You walk into the bathroom and smell the strong odor of bleach. Someone did some heavy cleaning in here recently. But they missed a spot. On the mirror of the bathroom, you see a faint, light brown streak. It could be dried blood. What do you do now?

Science at Work

Before forensic science was a common term for television dramas, the scene like the one above might have been of little use to the homicide detectives assigned to the case. Today, with the lighting-speed advancement of the forensic field, there are actually several processing techniques that could be used in the cleaned-up bathroom. The forensic evidence revealed by these techniques might lead to crucial investigative leads!

Types of Forensic Evidence

The following list will show you the different types of forensic evidence that are commonly found at crime scenes. Forensic Investigators will search for specific types of evidence based on the type of crime they are investigating. For example, it makes sense to look for bloodstains during a homicide investigation. But it makes more sense to look for fingerprints or touch DNA on a simple vehicular burglary scene.

Let's look at each type of evidence in detail:

DNA

DNA (deoxyribonucleic acid) is the building block of all living things. Every person has a unique code or pattern of DNA that can be found in the nucleus of most of their cells. Investigators can find perpetrator DNA in biological evidence left at a crime scene. DNA can be found in saliva, blood, sweat, seminal fluid, and hair. Forensic science has reached such an advanced level that touch DNA can be found on surfaces contacted by the perpetrator, such as door handles or light switches.

This advancement is made possible largely because of a special step that is now used in DNA analysis. PCR (polymerase chain reaction) is a process that scientists use to copy samples of DNA. So very small samples that would have been used up in the testing process can now be copied multiple times to make larger samples.

For example, in 2001, Gary Ridgway was arrested and charged with the serial murder of several women in the Northwest. A face had finally been put on the notorious Green River Killer. Investigators re-examined biological evidence that was collected in the 1980s and 1990s with new DNA technology and found Ridgway to be a match for biological evidence found on his victims.

Fingerprint

Fingerprint evidence is the most common type of forensic evidence and can be very important to all types of investigations. There are three types of fingerprints that forensic investigators look for: latent, patent, and plastic.

  • Latent fingerprints are invisible and need to be processed with powders or chemicals to be seen

  • Patent fingerprints are visible to the eye because the person who left them had something on his or her fingers when he or she touched the surface where the print is found

  • Plastic fingerprints are actually impressions that are created when someone touches a soft substance and he or she leaves the impression of their fingerprints in the substance

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