Any substance that is collected using scientific methods from a scene of crime such as blood, semen, or any trace material like hair, soil and so on which after analysis using scientific method, can be produced in the court of law to establish a person’s guilt or prove him innocent is known as evidence. Medical evidence helps in the investigation of both civil and criminal cases. It forms the link between crime and criminal.
There are different types of evidence like biological, physical, digital and proper collection. Preservation and packaging are the key factors as improper collection, packaging, and preservation can lead to sample loss, cross-contamination, decomposition, or sample degradation. In case of the death of a person, medical evidence is the most important evidence and is inevitable.
The medical evidence is examined using a post-mortem report. Proper preservation of medical evidence can help in DNA extraction and DNA profiling. The post-mortem report establishes details about cause of death and manner of death, including chemical and toxicological analysis, serological analysis, and DNA analysis.
While handling medicolegal autopsy cases, certain standard guidelines must be laid down to assist in selecting appropriate specimens or the body fluids and tissues for post-mortem biochemical and toxicological evidence. Many times an autopsy is conducted before all the circumstantial evidence is collected and investigated. Hence it is vital to preserve all the necessary samples at the time of autopsy.
Preservation of Medical Evidence
- The major evidence blood can be found is in either dried or liquid form or both. If dried blood stains are encountered at a crime scene that is present on a smaller cloth or material which is transportable, then place a paper on top of it and attach it to the object or material to prevent contamination and then fold and store it in a cardboard box or brown paper bag followed by sealing. If it is present on a non-porous surface, it can be lifted using conventional adhesive tapes or scraping. If a liquid blood sample is collected from the dead body, take 2-5 ml of intravenous blood and place it in clean, sterile vacutainers. Then add 4% EDTA.
- If any stained clothes are collected, then to prevent contamination and bacterial growth, air dry the cloth and then pack using paper. The use of polythene or plastic wraps will promote bacterial growth as it can retain moisture.
- Evidence such as bones should be air-dried, wrapped in kora cloth and placed in cotton cushioned cardboard boxes. If teeth as evidence are found and if it has root tissues attached, then separate the tissue and collect it separately and then air dry the teeth. It can be preserved by storing it in small, clean, sterile containers.
- In case of trace evidence like hair, it should be collected using pointed forceps, tape lifting, vacuuming and preserved in a druggist fold or a zip lock bag.
- Tissue, muscles, skin, organs should be preserved by adding suitable preservatives like normal saline or keep the tissue at -20℃. In cases of exhumation, dry tissues are placed in a sterile container without adding any preservative and kept at room temperature.
- When semen swabs or vaginal swabs are collected, they should be air-dried and stored in vacutainers at 4℃.
- For fetal samples, if it is an older fetus, then blood samples from heart puncture and in young fetus analysis of chorionic villi may provide the fetal pattern without maternal contamination. The whole body of the fetus can also be sent by preserving it using normal saline or DMSO saturated with NaCl. This jar should be placed in an icebox. If the fetus is macerated, then the most suitable tissue for DNA typing will be fetal lung and brain tissues.
- For toxicological findings, Vitreous humor, Cerebrospinal fluid, and urine can be preserved with NaCl, and Viscera can be preserved using rectified spirit or common salt.
- If death is suspected to be due to poisoning, then blood should be preserved as follows: –
- Frozen condition without preservative for volatile poison.
- Fluoride for alcohol.
- 1-2 cm layer of paraffin for carbon monoxide poisoning.
- 30mg of sodium citrate for 10 ml of blood in case of oxalic acid and ethylene glycol poisoning.
- 10 mg of sodium nitrate for fluoride poisoning.
Preservation of evidence is very important as it has a greater impact on the entire course of a case. If not appropriately preserved, it can give a false interpretation of the test results.
It is necessary to maintain a proper chain of custody to know who had charge of the evidence at any given point of time. It helps in preventing evidence from getting tampered with.