Crime scene evidence is all materials at a suspected crime scene, collected for the purpose of understanding what occurred and how it occurred. This evidence is also part of building an investigation that might be used to determine fault or guilt so that arrests can be made, and so that involvement of any suspects can be proven in criminal trials. What actually gets collected in crime scene evidence may be individualized to each scene, and no two locations where a crime has occurred, or no two crimes, are exactly the same.
Before investigators begin collecting crime scene evidence, attempts are made to keep the scene from becoming contaminated by unrelated material. Police will often rope or tape off areas so that strangers don’t walk through them, leaving DNA or other evidence. Still, it’s fairly easy for evidence to become convoluted, particularly if there is a live victim at the scene that needs medical attention. Other barriers to have the perfect and untainted scene can include rapid changes in weather and failure to discover a crime until some evidence has degraded. Moreover, some crimes have more than one scene or site, and areas where part of a crime has been commissioned aren’t always clear.
There are many types of crime scene evidence that might be collected. Finding fingerprints can remain an important tool in determining involvement of suspects. DNA collection is valuable too, and this might be obtained by gathering samples of blood, hair, saliva or other fluids. Evidence of weapons, either the weapons themselves or things like bullets that are left behind are of value. Additional items that might need to be collected are clothing, evidence of any drugs/alcohol or unknown substances, and any other thing that might signify intent, explain a crime or point to possible suspects.
Investigators usually have a variety of ways to collect crime scene evidence. They often take photographs and they may remove and bag any small or larger items that could have something to do with a crime. Things like fingerprint and DNA samples are obtained in small amounts. Each investigatory agency possesses standards on what to take and how to collect it. This helps provide consistent efforts in crime scene collection and greatly reduces possibility that in collection efforts, investigators will accidentally or purposefully contaminate a crime scene.
Crime scene evidence collected isn’t always sufficient and early collection efforts don’t necessarily solve crimes. Investigators must sift through collections trying to determine what is relevant, and this can be challenging. What are looked for, though, are patterns suggesting motives, suspects, or commission of a crime. While sometimes these patterns are obvious, other times they may not become obvious until investigation beyond crime scene collection occurs.