Fighting Crime with Analytical Chemistry
Igor Lednev, University at Albany, NY, USA, is a crimefighter, neither in the traditional sense of “officer of the law” nor as a caped crusader, but as a chemist working on analytical techniques that give law enforcement the necessary tools to extract solid (or liquid) evidence from a crime scene and to characterize and date the samples. In earlier work, amounting to some fifty-plus published peer-reviewed papers, Lednev has tackled the issue of how to analyze bodily fluids, blood, sweat, saliva, and seminal and vaginal fluids and secretions.
Ledenev and colleagues have added a new rather important analysis to their forensic arsenal: a technique for determining how old a blood stain found at a crime scene might be. The research uses the team’s patented laser technology and could soon help law enforcement catch criminals.
Non-Destructive Age Testing of Bloodstains
Raman spectroscopy and advanced statistics allow the researchers to date a blood stain accurately, provided said blood stain is less than two years old. Raman spectroscopy involves shining a laser on a sample and measuring the intensity of scattered light. No two substances give the exact same Raman spectrum and so the spectrum is essentially a unique fingerprint for a given material. Importantly, from the criminal evidence point of view, the process is non-destructive. Thus, it can be repeated at any time, and also allows other tests, such as DNA sequencing, to be carried out.
In a proof of principle, Lednev’s team had collected fresh blood two years ago at the start of their experiments from two healthy adults (a man and a woman). They dried the samples to simulate a crime scene blood residue and then analyzed the samples at 15 different times over the two-year period. They were able to provide an age for any given sample with an accuracy of 70 % and could distinguish between stains aged hours, days, weeks, or months. At the moment, crime scene investigators have no single validated approach to determine when a blood stain might have been deposited, which could, in theory, lock down a case or exclude a suspect.
“Determining the time at which a crime occurred and the order of events at the crime scene can be challenging, especially if no reliable witnesses are available,” Lednev explains. “Blood is the most common body fluid found at the scene of a violent crime, and can be the most valuable in the amount and types of information it can provide.”
Easy-to-Use Handheld Tool as the Goal
The team hopes to ultimately develop a “point and shoot” Raman spectroscopy instrument that could be used by law enforcement officers at a crime scene to quickly analyze a whole range of biological stains and deposits. Also in their arsenal of analyses is one that can quickly reveal whether a sample is human or animal, another one can distinguish gender and the possibility of determining the age of a suspect or victim is under investigation.
“We are demonstrating the ability for law enforcement to obtain key information and specific characteristics (age, race, sex, etc.) by simply scanning a biological stain at the crime scene,” Lednev adds. “Our tool would significantly narrow down the search for a suspect or victim.” He hopes to see a handheld Raman instrument being commercialized within three to five years.
Expanding the Model
“We still have the samples and we keep doing measurements, but it is too early to tell whether we will be able to estimate time since deposition (TSD) with a satisfactory accuracy beyond two years,” Lednev told ChemViews Magazine. The bloodstain aging process depends strongly on environmental conditions and the team has investigated the stains in an indoor environment at room temperature, under normal humidity, and in the absence of direct sunlight. “We plan to expand our study and develop the TSD prediction model for other common conditions including elevated and low temperatures, and high humidity,” Lednev explains.
In the broader picture, the various spectroscopic-statistical models that the team has developed so far allow them to determine the type of body fluid, differentiate menstrual and peripheral blood (important for rape cases), as well as human and animal blood. They have also reported proof-of-concept studies on differentiating race and sex based on body fluid traces. “We plan to develop a cascade statistical model incorporating the individual models,” the team concludes.
- Predicting the time of the crime: Bloodstain aging estimation for up to two years,
Kyle C. Doty, Claire K. Muro, Igor K. Lednev,
Forensic Chem. 2017, 5, 1–7.