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The Value of a Lasting Impression Forensic scientists rely on a variety of evidence to participate in the crime investigation process, as well uphold justice by helping to bring about convictions for the guilty and acquittals for the innocent. Among the different types of evidence that investigators collect, analyze, and record is impression evidence, which encompasses any markings that are produced when one object comes into contact with another, leaving behind some sort of indentation or print—an “impression.” According to the National Institute of Justice, impression evidence is one of the most common forms of evidence that investigators may detect and collect at a crime scene. It can be either two-dimensional or three-dimensional, encompassing fingerprints, bite marks, footprints, tool marks, and tire marks. Impressions get left behind in or on a wide variety of different materials at crime scenes, which can affect the methods used to collect and preserve said evidence. From within a collection of impression evidence, forensic scientists can further detect different types of patterns that provide identifying information related to the object that left the mark and potentially its owner. Shoes, tires, tools, and fingerprints all have unique patterns that can help investigators narrow down their search for a suspect, or help link a tool to a particular crime. In many cases, the term “impression evidence” is meant to encompass pattern evidence, although they are technically two distinct yet related categories. Tires, tools, and shoes leave impressions that are categorized as “class evidence,” meaning they have characteristics that place or restrict the evidence to a particular group of objects, such as trucks, pliers, or boots. “Individual evidence,” on the other hand, such as fingerprints, possesses characteristics that can narrow it down to one specific person. Sometimes impression evidence may have both class and individual characteristics. For example, if a tool used for a crime has a unique flaw that affects the impression or the pattern within it, then tool mark examiners could use that information to not only determine the tool that left the mark but possibly also help link one specific tool to the crime. Regardless of whether it has primarily class or individual characteristics, each piece of evidence is valuable in its own way. It can prove certain facts

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