Massachusetts Criminal Lawyer Explains:
Preserving evidence should be the top priority of those entrusted with gathering and collecting evidence. Evidence collection protocols apply to both pre-collection and post-collection evidence. If evidence is not properly preserved prior to collection, it may be contaminated or destroyed. If evidence is not properly preserved and stored prior to forensic analysis or testing, it may deteriorate, destroying or devaluing it as a source of information.
Those responsible for collecting evidence must understand and employ a variety of evidence preservation protocols, depending on the type of evidence. Nevertheless, some guidelines apply to all evidence, such as limitations on the number of individuals allowed to handle the evidence, use of safeguards to minimize contamination, proper collection documentation, acceptable chain-of-evidence documentation, and evidence appropriate storage. As evidence collection methodologies improve, forensic experts develop new protocols to preserve that evidence.
Memorializing the Crime Scene
To preserve the appearance of a crime scene, as well as the loci of relevant objects to one another, a crime scene investigator should photograph the crime scene. To improve the usefulness of the photographs for later examination, the investigator should photograph the area from various angles and distances. To give these photographs additional meaning, he should illustrate the scene with a scaled drawing. Further, he should memorialize in writing important impressions, observations and measurements of the scene that photographs cannot capture or record, including smells, temperature, and humidity.
Basic Protocols for Handling Evidence
Depending on the circumstances, an investigator may need to wear a sterile suit covering his body, hair, and shoes to prevent him from contaminating the evidence with his own DNA or any other trace evidence he might otherwise transport with him to the scene. At almost every crime scene, he will wear latex or chloroprene gloves, and change them often during the evidence collection process. These gloves not only help safeguard the crime scene from contamination, but protect the investigator from potentially harmful bacteria and toxic debris. Additionally, to reduce the amount of dusts and mists from fingerprint powder or chemical processing and putrid decomposition odors he might otherwise breathe in, an investigator may wear a respirator.
Ideally, an investigator should carefully collect the most fragile evidence first, before disturbing the scene by removing larger, heavier, or less fragile evidence. Otherwise, an investigator should begin by systematically collecting the “top” layer of evidence, allowing him to then memorialize or photograph what he finds beneath that evidence. An investigator should collect evidence in a sterile, careful, and precise manner, using sterile instruments, such as tweezers.
An investigator should place most evidence into paper containers, such as bags and envelopes; evidence packaged in plastic bags may be exposed to moisture, hastening deterioration and risking environmental contamination, such as mold, and the destruction of useable DNA or other trace evidence. Investigators should not package moist evidence until it is thoroughly dry and or seal collection bags or envelopes prematurely. Most evidence should be stored at room temperature, unless it is liquid evidence, in which case it should be refrigerated and packaged in a sterile glass or plastic bottle.
An investigator is responsible for appropriately labeling all evidence collection containers with the case number, collection location, date and time, and his identifying information. He should log all collected evidence on a separate document, for later reference.
To establish proper chain-of-custody of the evidence, investigators must track the evidence from place to place, documenting who retrieved, handled, transported and received the evidence, specifying all dates and times.
Without a proper chain-of-custody documentation, a court may rule the evidence hopelessly compromised and inadmissible at trial.