Crime Scene Evidence
Items of physical crime scene evidence are not always visible to the naked eye and may be easily overlooked. A deliberate, methodical, disciplined approach to collection and preservation of evidence is essential. One exception may be if crime scene evidence integrity is at risk, and under those circumstances it is important that rapid decisions be made to prevent its degradation and/or loss.
It is imperative that the crime scene investigator obtain as much information as possible regarding the circumstances of the crime prior to entering the scene. Statements from witnesses, victims, or first responders can provide a broader understanding of the investigation.
The investigator can develop an approach to the scene based on this information and the nature of the crime. For example, at the scene of a burglary, attention may focus on the point of entry. Fragments of wood, metal, or broken glass may be discovered, along with fingerprints, blood, and fibers from clothing deposited when the perpetrator forced entry.
In the case of a violent crime such as a sexual assault, attention may be directed to the clothing and the person of the victim(s) and the suspect(s). An investigator might find body fluids, stains, torn clothing, fingerprints, fibers, hair, and other trace materials in the areas where the attack took place. Potential crime scene evidence such as saliva, bite marks, semen, hair, skin tissue under the finger nails, and other trace materials may be found on the victim(s).
Transferred evidence such as cosmetics, vaginal fluid, hair from the victim, and blood may also be found on the suspect. Once potential evidence is located and documented, the next step is to collect and package the items in a manner that prevents contamination, loss, and deleterious change.
Biological crime scene evidence requires care to guard against the possibility of cross contamination either by the investigator or by other biological specimens at the scene. Equipment is available to crime scene investigators which aide in the prevention of cross contamination.
Types of equipment include:
The forensic investigator should prioritize the order in which evidence is collected. Biological evidence, trace materials, and evidence of a fragile nature should be collected first. Collection methods used to gather and package this crime scene evidence vary. The use of an alternate light source (ALS) or oblique lighting may be necessary. A sample detected with the ALS should be properly packaged with a notation alerting the analyst that it is a luminescent sample.
Preservation of Evidence From crime scene to forensic laboratory to courtroom, all evidence must be inventoried and secured to preserve its integrity. Crime scene evidence admissibility in court is predicated upon an unbroken chain of custody. It is important to demonstrate that the evidence introduced at trial is the same evidence collected at the crime scene, and that access was controlled and documented.
An understanding of the rules governing chain-of-custody is vital for an investigator. For example, in a sexual assault incident, the victim is typically transported to another location to have a sexual assault examination performed. Many jurisdictions have established teams to perform these examinations, and they go by several names, such as: Sexual Assault Victim Examination (S.A.V.E.), Sexual Assault Nurse Examiners (S.A.N.E), Sexual Assualt Response Team (S.A.R.T) . The examination involves the collection of the victim's clothing, hair samples, swabs for body fluids, and documentation of bruising and bitemarks. The materials collected are packaged by the team members.
Proper evidence packaging includes: Appropriate packaging and labeling of all items, each item properly sealed and marked and correct and consistent information recorded on label and procedural documentation.
The evidence is turned over to the investigator for submission to a department's property and evidence section. A receipt documenting the transfer is obtained. Generally, submissions to the forensic laboratory are done on a request for analysis form, listing the evidence items, and a documented chain of custody. Each individual assuming custody of the evidence from collection through analysis signs the chain of custody document. Many departments have automated this process using an information management system, whereby all transfers are securely done using barcodes. The chain of custody report will identify each individual contributing to the analysis of the evidentiary materials.
Once the analysis is complete, the evidence is either returned to the submitting agency or stored by the laboratory. The chain of custody will document this disposition. All law enforcement reports, photographs, lab analysis reports, and chain of custody documents are kept in the case file, which can be made available to the prosecution and is subject to discovery by defense counsel.
Think of the chain of custody as a chain, if one link should be broken, the chain is broken, and the evidence collected may be ruled as inadmissible.
Hints To Safeguard The Chain of Custody:
Limit the number of individuals handling evidence.
Confirm that all names, identification numbers, and dates are listed on the chain of custody documents.
Ensure that all evidence packaging is properly sealed and marked prior to submission.
Obtain signed or otherwise secure receipts upon transfer of evidence.
(Information provided by the Department of Justice)
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