READ: Class vs. Individual Evidence

READ: Class vs. Individual Evidence

Evidence can be classified into two different categories: Class Evidence and Individual Evidence. Each type of evidence and several examples are described below. 

Class Evidence

Class evidence is any evidence that can only be associated with a group of items that share common properties. For instance, a print made in the dirt from a brand new shoe would be considered class evidence. Investigators would be able to determine what type of shoe made the print, the size of the shoe, the brand of the shoe, where the shoe was manufactured and sold, but they would not be able to prove with 100% certainty that it was worn by an individual person.

Other examples of class evidence would be things like pieces of fabric fibers found at a scene, particles of dirt, bullet casings, pieces of tape with straight cuts or tears, etc. 

Individual Evidence

Individual evidence is any evidence that can be associated with an individual source or person. For instance, a print made by an old worn out shoe would be considered individual evidence. In addition to all the information that investigators could determine if the shoe was new, they would also be able to see wear marks on the print. Wear marks on the print could be matched to a shoe taken from a suspect. Individual evidence always involves the comparison of the evidence found at the scene with items from the suspect or the scene. Individual evidence allows investigators to prove with 100% certainty that an item came from a specific source or person. 

Other examples of individual evidence would be things like fingerprints, DNA, bullets with markings made by the barrel of a specific gun, toolmarks with characteristics that can be matched to a specific tool, tape or paper with unique tears, etc. 

Value of Evidence

After reading about both of these types of evidence, it may seem like class evidence doesn't have much value since investigators can't prove that it came from an individual person or source, but class evidence can be useful especially when investigators find multiple pieces of class evidence.

For example, investigators might find a print from a new Nike running shoe size 9 at a scene, a few pieces of blue electrical tape, and some paint from a 2003 Red Ford Taurus. Individually these pieces of evidence might not mean much; many people have those same running shoes, and many people have blue electrical tape, and many people own a 2003 Red Ford Taurus. Individually it is impossible to prove that these items came from a certain person, but if you consider the items together, the likelihood that someone owns those shoes, that brand of tape, and has that specific car becomes much less likely. So, if investigators can prove that the suspect owns those running shoes, has the tape and has that car, it becomes much more likely that the items indicate that the suspect was at the scene.

In the video below, a forensics professor explains more about class and individual evidence and gives some additional examples. 

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