Forensics Q&A: Chain of Custody

By Kristy Lahoda | @KristyLahoda

Disclaimer: The information provided in this post should not be used for malicious intent unless it is in the form of crime writing. The author is an explosives expert, not a crime scene expert. While every attempt was made to ensure the accuracy of this information, for security purposes, some details may have been withheld.

QUESTION: In my crime novel, there are scenes involving courtroom testimony about the evidence that was collected at the crime scene. What happens to evidence at a crime scene once it’s been collected?

ANSWER: An investigator from the agency that had jurisdiction over the crime scene will take the evidence to the proper lab. Depending on the state, it could be the state crime lab, state highway patrol lab, state fire marshal’s lab, a city or regional crime lab, or even governmental labs such as the Federal Bureau of Investigation, the Drug Enforcement Agency, or the Bureau of Alcohol, Tobacco, Firearms and Explosives. It really just depends on the jurisdiction. 

So what is chain of custody?

Chain of custody provides a record of time and possession/location of the evidence. This is documentation that later becomes important if the case goes to trial. If the evidence cannot be accounted for from cradle to grave—from detection at the crime scene, to delivery to the crime lab, to analysis, and to either destruction or its return to the submitting agency—it is impossible to prove that the evidence has not been tampered with. This is often a tactic of the defense attorney and rightfully so. The evidence needs to stay secure at all times. 

How does a crime lab keep track of chain of custody?

Once the evidence is collected and packaged, the investigator secures it with evidence tape, initial and date it, and bring the packaged evidence to the lab from the crime scene. Paperwork is submitted with the evidence that provides a description of the evidence in each container along with the type of evidentiary tests that the investigator wants run on the sample. For example, if the investigator suspects that an item of evidence was used to commit arson and this item potentially has latent prints on it (such as a gas can), then there will be an indication such as checked boxes that will let the lab analysts know to analyze the evidence for arson and latent prints.

In many crime labs, each piece of evidence is received and logged into the Laboratory Information Management System (LIMS) by the evidence-receiving technician. The investigator’s name and submitting agency will be on the evidence receiving form and once the evidence is logged into the LIMS system, it will be transferred from the investigator’s possession to the evidence storage area. Once the lab analyst wants to analyze the evidence, he or she will first transfer it into his or her possession, then cut through the evidence tape, breaking the seal. After analysis, the lab analyst will place the evidence back in the original container, add another piece of evidence tape to seal the package once again and write his or her initials and possibly the date. The initials are written half on the tape and half on the package. The evidence is then transferred back into the evidence storage area. Each transfer is logged into the LIMS indicating the time and date of transfer.

What happens if the chain of custody is broken?

If proper chain of custody is not documented and maintained, there will most likely be serious repercussions for the case in court. This could lead to the perpetrator being found not guilty even if s/he was actually at fault for the crime. 

Kristy Lahoda, Ph.D., is an explosives analyst contractor in a crime lab as well as a science content editor for a major educational publishing company.  She writes Christian forensic suspense and discusses forensics on her blog called Explosive Faith.  You can follow her on Facebook and Twitter.

If you have a forensics question for Dr. Lahoda that you'd like to see answered on the QueryTracker Blog, send your question via Carolyn Kaufman using the email link under Contact Us in the right-hand column of the main QTB page.