Trace evidence is best described as any small piece of evidence that has to be collected by Scenes of Crime Officers (SOCO) and places a suspect at the scene of a crime.
What is Trace Evidence?
Trace evidence normally takes on the form of one of the following:
- Blood Flecks
Trace evidence can sometimes be minute and can be difficult to detect, which is why a crime scene is sealed off only to those people who are responsible for overseeing the collection of physical evidence in whatever form it takes.
Normally these Scenes of Crime Officers (SOCO) are dressed in protective clothing so that they neither contaminate the crime scene nor disturb evidence that may be already there. This protective clothing normally takes on the guise of a protective plastic suit, gloves, head covering and footwear protectors that are all designed to stop hair, fibres and skin from transferring from the forensic scientists into the surrounding crime scene. Police officers also attending the crime are required to wear this protective clothing for the same reason.
How Trace Evidence is Collected & Tested
Trace evidence is collected at the scene and is also collected from the deceased post mortem. This is done by scraping the fingernails, checking clothing for fibres and also checking footwear for soil samples that might allude to whether or not the victim’s last living moments were spent somewhere else before being moved.
It is not uncommon for the perpetrators of the act of murder to move their victim to try and slow down the process of identification and also to remove suspicion from themselves. In many murder investigations it is common for the victim to have known the killer so their surroundings can sometimes be something of a giveaway and therefore moving the body post mortem to another locale is an attempt – albeit mostly a futile one – to cast doubt elsewhere.
As mentioned already there are many different types of trace evidence that can be collected; for the most part a forensic scientist or pathologist will look for signs of a struggle which can lead to the discovery of skin particles, blood flecks, hairs or fibres being transferred by contact from the perpetrator to the victim.
Where hair has been found it can be tested not only for a DNA match but also for trace elements of various chemicals which are found in hair care products; identifying such products can give an indication as to the sex of the assailant.
Grass, glass and soil traces are also an important element of the crime scene environment and each of these trace elements should be given due care and attention as they can often lead to surprising revelations and also bring avenues of investigation to the fore that would have not previously been considered as viable options.
Every Scene of Crime Officer (SOCO) responsible for the collection of material at a crime scene will spend many hours meticulously combing it for signs of this trace evidence and will spend equally as much time within the laboratory referencing and cross referencing this material in order to build up as comprehensive a picture of the crime scene and the events that unfolded there.