Please note: This document has been google translated from original publication which can be found here
Police and NFI make grab marks visible on clothing
The police, the Police Academy and the Dutch Forensic Institute (NFI) are collaborating on a pilot project to visualize hold traces on clothing. The more visible a few trace of an (unknown) offender, the greater the chances that forensic experts can secure DNA.
All sorts of things are conceivable in which the method can play an important role. For example, a wandering woman being attacked from scratch or a young girl being pulled and misused her bicycle.
“The perpetrators thereby grasping the clothes of their victims and leave it behind DNA. Such an event could for victims are so significant that they do not know what exactly happened and therefore not exactly where they are grasped, “Kim van den Bogaert explains. She’s investigative expert from the Forensic Investigation by the police central Netherlands and did in the past year extensive research on the display of grip rails.
In those cases, the police can do an undirected DNA-sampling. But the chance of a successful sampling is not much bigger when you can make the handle visible traces of the perpetrator and focused can be sampled?
How long will hold a trace visible?
Visualization of grip tracks is no stranger to discipline under forensic investigators. But for visualizing fingerprints on porous surfaces such as cotton and polyester had been little research. Earlier research showed that the so-called metal deposition is the best method to visualize grip marks on textiles.
But how long after the crime, you can still use this means? And you can make better DNA profiles through this method than if the victim indicates he or she is about gripped? With these two questions Laney went to work. Her research carried out at the NFI, in cooperation with the product Finger Traces Biological traces. Researcher Matthijs South Mountain coordinated the research.
NFI’ers in white shirts
“We asked people if they white polyester and cotton shirts would wear. As they walked around in a day or two, “says the researcher. At different times we have ‘evaporated’ the shirts to make the handle visible traces; So after one day, one week, one month and after three months. ”
Several NFI’ers demand were to indicate what they thought were the grip tracks. “Per shirt I have asked three employees. If two of the three grip track were able to identify, we have it listed as a recognition of the grip track. ”
One or two days after the gripping, most grip traces appear to be recognized. Even after a week, month hold traces in many cases still seen. “Even 11 of the 24 tracks were seized on cotton shirts still detected after three months. Polyester was lower though. ”
Laney also examined whether a more targeted sampling DNA from a turn. “That proves the case. With targeted sampling is on average 45 percent of the detected DNA from the perpetrator. In an undirected sampling is 25 percent. It differs certifying that you pick up more DNA from the victim in an undirected DNA sampling (36 percent) than among targeted sampling (15 percent). ”
Moreover, according to the expert investigation, the method of metal deposition is not harmful to the DNA. “So there’s always a later undirected sampling a larger share of the shirt as possible.”