Class evidence is material in a criminal investigation that can be linked with a group of people, but not a specific individual. This type of evidence may be used to narrow down a list of possible suspects. In combination with other evidence in a case, it can demonstrate that a limited number of people had all of the characteristics associated with evidence left by a perpetrator. This is in contrast with individual evidence, which is materials that are linked to a particular person.
When investigators arrive on a scene, they collect as much evidence as possible so they can gather information about a case and, ultimately, build a case for court. This includes taking note of anything unusual or anything that could be used for identification. A common example of class evidence found at crime scenes is impression marks such as footprints, tire marks, or marks left by tools.
This evidence can help investigators pinpoint a brand or type of product involved in a crime. This can be used to learn more about who would be a likely candidate as a suspect. Sometimes, class evidence can become individual evidence. For instance, shoes and tires both develop unique wear patterns over time. Investigators can inspect the evidence closely to see if there are tell-tale signs of wear that could be used to link a particular person to a crime scene, rather than any person meeting a rough series of parameters.
In investigations, class evidence can be very valuable. It helps investigators quickly narrow down a list of potential suspects by excluding people who do not meet the parameters set by the evidence. The more quickly a suspect is identified, the more likely it is that additional evidence can be uncovered. This evidence can be used to confirm that a suspect is probably behind the crime so that a successful prosecution can occur in court.
Individual evidence is stronger in court, but class evidence can still be useful. It can be used to show how investigators developed lists of likely suspects. Sometimes a combination of class evidence can be quite compelling for a jury as well, by showing that there are very few people who satisfy characteristics determined by multiple pieces of evidence. People who are accused are permitted to examine class evidence and to bring in experts of their own to testify about the evidence, its validity, and its applicability to the case in question.