Protecting Evidence From a Crime Scene

¶ … physical evidence include: trace evidence, impression evidence, and biological evidence.

Several examples of physical evidence include: Biological material such as blood, saliva or semen; fingerprints; hair; and fibers. Physical evidence is that evidence that consists of tangible materials such as paint, glass, ballistics, dust, dirt, and wounds (www.nfstc.org). Impression evidence is also physical evidence and it can be tire tracks, prints from shoes or boots, bite marks on a victim's body, and tool marks (for example, nicks and chips from a certain tool that was used to break into a building are part of impression evidence).

How is evidence collected, packaged, and preserved?

The Oregon State Police Forensic Services Division offers "General Evidence Guidelines" -- and the report asserts that all evidence has to be collected, handled, and stored in such a way as to "ensure" its integrity. The guidelines are presented in bullet points, and will be presented here: "Protect yourself and others"; "protect the evidence"; "consider all types of forensic evidence"; "chain of custody starts at the crime scene -- keep it short"; "document location with notes, sketches, and/or photographs"; "mark evidence and packaging with your case identifier, initials, date, and description of evidence"; "package all evidence separately"; "allow wet biological stains to air-dry"; "obtain standards if needed for a comparison of evidence"; "use packaging that is appropriate for the type of evidence (paper bags, envelopes, plastic bags, cardboard boxes, tamper-proof sealing…" (Oregon State Police).

The National Forensic Science Technology Center (www.nfstc.org) suggests that in order to avoid cross-contamination while gathering evidence, the investigator has to be sure his or her tools are absolutely clean, that gloves are changed each time a new sample is collected, and that gathering evidence in its original state. What that means is, "the entire object" should be collected and packaged, unless it is too big to be practical (www.nfstc.org). The collection of blood should be done by removing "a section of the item" with the bloodstain using a "sterile or clean cutting device"; or the sample can be scraped with a razor blade onto a clean piece of paper; or "fingerprint lifting tape" can be placed on the dried blood stain and lifted off (www.nfstc.org).

Packaging evidence and storing evidence is absolutely vitally important in order to preserve evidence properly for presentation in a court of law. Biological evidence should be dried prior to packaging in order to "minimize sample degradation" (www.nfstc.org). Paper is preferred as a material to be used to package evidence, but there are crime labs that package in "plastic if the sample is thoroughly dried" (www.nfstc.org). As for liquid samples, like water from a toilet bowl or from pipes, needs to be accurately documented and "packaged in a sterile glass or plastic container and refrigerated as soon as possible."

Preserving evidence so that it is not contaminated between the crime scene and the courtroom also means there must be an accurate inventory and there must also be an "unbroken chain of custody" (www.nfstc.org). As to the chain of custody, every crime lab has a "secure electronic chain of custody record through the Justice Trax Laboratory Information Management System (LIMS) (www.nfstc.org).