Bloodstain reveals the time of a crime
As a bloodstain ages the structure of the Raman spectroscopy signal varies in a tell-tale manner
Chemical changes as bloodstains age could pinpoint the time of a crime for up to two years
A new tool for estimating the time of a crime from bloodstains that are up to two years old could soon be a reality for forensic science. The technique analyses the interaction of light with the chemicals in a sample, using a process known as Raman spectroscopy. It is a major leap forward from current techniques that can only date a bloodstain within around one week after a crime.
In addition to its simplicity, this innovation offers two major advantages over existing methods for dating a death or an assault. First, it does not require the presence of a body or surviving victim. And second, it is non-destructive, meaning that it leaves blood samples intact for other analysis.
“Our work is a vital step forward that could help solve criminal cases,” says Igor Lednev, who is developing the technique with recent PhD graduate Kyle Doty at the University at Albany of the State University of New York, United States. Their proof of concept study is published in ForensicChemistry.
Blood is a complex biochemical mixture that begins to change in many ways from the moment it leaves the body. Rather than attempting to identify specific chemical changes in the blood, the researchers simply allowed bloodstains to age on a laboratory bench and analyzed the development of the Raman spectroscopy signal over time. The results at selected times are displayed as a series of peaks indicating the intensity of the signals at different wavelengths of light.
Lednev says that the observed variations are significant enough to distinguish between bloodstains differing in age by hours, days, months or years. He and his team next plan to look at the effects of different surfaces carrying the blood, and the conditions, such as temperature and humidity, in which it ages. They will also investigate the differences between blood from people of different sexes, ages, and races. Blood from people with specific diseases will be another more subtle factor to add
to the analytical mix.
This work on blood is part of a wider effort to improve forensic analysis techniques using Raman spectroscopy. Lednev and his colleagues have been working on this for many years. They are developing a suite of techniques to analyze all the major bodily fluids – blood, saliva, semen, sweat, and vaginal fluid. “In the near future we hope that our methods will be used in actual forensic casework to provide investigators with more beneficial information than is currently available,”
Doty, K.C. et al.: "Predicting the time of the crime: Bloodstain aging estimation for up to two years," Forensic Chemistry (2017)