2.03 Physical Evidence

Physical Evidence

Physical evidence is also known as indirect evidence and is defined as an object(s) related to a crime that helps determine what happened. Physical evidence is any material item found at a crime scene that can link a suspect, crime scene, and/or victim. Trace evidence is a type of physical evidence that is small, often microscopic. Physical evidence is more reliable than testimonial evidence because it can be tested scientifically and does not lie. Remember evidence is defined as anything that tends to disprove or establish a fact.

Examples of physical evidence include but are not limited to:

• DNA
• Fingerprints
• Trace Evidence: Hair, fibers, glass fragments, soil, powders, body fluids
• Tire tracks and other impressions
• Blood spatter
• Bullets

Physical evidence is important in proving a crime was committed and can determine whether someone is telling the truth or not. Physical evidence is tested by the forensic scientist. An unknown sample (physical evidence) found at a crime scene is compared to a known sample by the forensic scientist. Physical evidence can be used to create a reconstruction theory. You may know these as a reenactment of the crime if you watch the TV shows about crimes. Physical evidence can also link a person to a victim or crime scene. This is known as Locard's Exchange Principle.

The Locard Exchange Principle was discovered by a French professor named Edmond Locard. He is also considered the father of criminalistics. The Locard Exchange Principle says that whenever two objects come in contact with each other, traces are exchanged. For example, when you hug your friend in the hallway at school, traces such as hairs and fibers are exchanged from you to your friend and vice versus. This principle links suspects to the crime scene or to the victim.

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Evidence Classifications and Distinctions

Watch Evidence Classifications and Distinctions below.

Evidence Classifications and Distinctions

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Class vs. Individual

Physical evidence can be considered class or individual evidence. Evidence can have both class and individual characteristics depending on the type of evidence. For example, a piece of hair evidence can be considered class evidence if no root is attached but if a root is attached and DNA can be obtained it is considered to be individual evidence.

Class evidence is any item that is considered common or mass-produced. One common example of class evidence is a fiber. Think of how many thousands of yards of that fabric were made. Other examples of class evidence are small fragments of glass that could not be matched to a particular source, powders, and hair without the root attached (all brown human hair has the same class characteristics under a microscope).

Individual evidence can identify the source and be considered unique. Examples of individual evidence are DNA, skin cells, hair with the root attached, fingerprints, shoes that have been worn for an extended time, dental impressions/marks, large pieces of glass that can be matched to another piece of glass, and any type of tear patterns that can be matched together.

Read The Characteristics of Physical Evidence to see more examples and to understand more about the difference between class and individual evidence (characteristics).

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