The chain of custody is a group of documents aimed to ensure that the sample acquired by the forensic operator arrives intact at the laboratory, where it will be the object of subsequent laboratory examinations. Chain of custody allows the tracking of samples at all times and in all phases. It includes photo and video graphics documentation of all the steps the given source of biological evidence under investigation goes through. It begins when the operator collects the findings/samples and ends when it is analyzed in forensic laboratories.
The finding and preservation of the sample are critical to obtaining reliable results from subsequent DNA analysis.
The forensic operator must ensure that each finding/samples, after being collected, is placed in a container that is both suitable for the preservation of the acquired sample and ideal for the type of container sealing chosen.
The hair must be very carefully collected without damaging the bulb, which is the terminal part of the hair containing DNA and is valuable for subsequent genetic investigations.
Also read: Common FAQ related to Forensic Science
Hair and fiber samples are taken only if the transport of the entire finding is not possible or if they can be assumed to be lost by moving the object itself. Hairs and fibers can be found easily on some surfaces because they are visible to the naked eye.
The acquisition of the single hair formation or fiber should preferably be performed with sterilized tweezers, better steel than single-use, because of the electrostatic phenomena that can occur with contact with the hair formation.
Using sterile tweezers, the sample (hair or fiber) is collected, removed from the surface of the finding, and carefully placed in a clean paper bag that is usually folded and placed in a sterile single-use tube. An alternative method often used is the collection of hair and fiber using adhesive tape. The tape is applied directly to the finding, removed, and properly packed into a sterile single-use tube. Then, the tubes referring to an individual finding are placed and secured in a security bag with a corresponding security seal.
Every evidence bag must have its chain of custody form, and each time the charge of evidence is changed, an entry of signature, date, and time is necessary for the chain of custody form.
The chain of custody form shall include the following information:
- Unique identifier
- Name and signature of the operator
- Name of the recipient
- Laboratory’s address
- Details of each sample (with time/date of collection)
- Signatures of everyone involved in the chain of possession with date and time
- Time, Date and method of delivery
- Any other information about the sample
So, the chain of custody maintains the integrity of the sample. The traceability of the record of the control, transfer, and analysis of samples indicates the transparency of the procedure.
For these reasons, genetic results (DNA) from laboratory investigations from the findings/samples acquired on the crime scene have no significance in Court unless there is appropriate documentation that allows the sample from which the data was generated to be traced at any time.
- The Importance Of Hair As Biological Evidence In Forensic Science. https://forensicarticles.com/the-importance-of-hair-as-biological-evidence-in-forensic-science/
- Chain of Custody Article – StatPearls. https://www.statpearls.com/articlelibrary/viewarticle/19272/
This article is written by Ms. Chiara Lucanto. She is a Forensic Biologist.