Improved Analysis of Bloodstains at Crime Scenes

Analyzing bloodstains at crime scenes can play a key role in law enforcement efforts to identify criminals. Current testing methods however are not without their limitations, and improvements could help forensic practitioners to learn more about a suspect in a shorter timescale.

Research published recently in Forensic Chemistry demonstrates the use of Raman Spectroscopy to estimate the age of bloodstains, an approach which offers several advantages. To learn more about the technique and discuss the type of information that can be obtained using this method, we spoke to the University at Albany’s Professor Igor Lednev, Kyle Doty and Mike Nolan.  

What information can currently be obtained from bloodstains at crime scenes, and what are some of the limitations of the methods used?

Currently, bloodstains discovered and collected at crime scenes can be analyzed to obtain a wide variety of information. Typically, a presumptive test kit will be used first (sometimes directly at a crime scene) to quickly determine if a stain is in fact blood. However, these tests suffer from a few drawbacks, including (i) false positive identifications (i.e. positive identification as human blood for substances that are not actually human blood), (ii) utilization of hazardous chemicals for the analysis, (iii) they are a one-time use approach so they can expire and need to be replaced often, (iv) they are specific to one particular body fluid so a different kit is needed for each body fluid, and (v) they consume a portion of the sample. Confirmatory test kits can be used, in addition to or in place of, presumptive test kits, which can also identify that the bloodstain is of human origin and not from an animal. Although confirmatory test kits do not suffer from false positive assignments, many have a lot of the same drawbacks as presumptive test kits. A full DNA profile can also be obtained from evidentiary bloodstains, which can identify a specific individual, or, by obtaining a mitochondrial DNA (mDNA) profile, the maternal lineage can be determined. More recently, new technologies have been developed to obtain specific identifiable genetic information (i.e., hair color, eye color, race, diet, etc.) about a person from bloodstains. However, these methodologies also consume part of the sample, which is preferably avoidable from a forensic standpoint. Most importantly, these methodologies are cost and time consuming that leads to significant backlogs of evidence, which has never been processed, in crime laboratories.

Can you tell us about your recently developed Raman method and some of the advantages it brings?

Certainly. Our most recent development is the ability to estimate the amount of time a bloodstain has been left on a surface, or what we refer to as the time since deposition (TSD), for up to two years. This approach introduces a significant advancement over what has been demonstrated previously, particularly with using Raman spectroscopy and chemometrics (i.e., statistical analysis applied to chemical data). The advantages of our approach are that (i) Raman spectroscopic analysis is a non-destructive technique, meaning that the samples are preserved for further testing (if necessary), such as obtaining a DNA profile, (ii) bloodstains can be analyzed quickly (in a matter of seconds), (iii) the results are supported with high statistical confidence, and (iv) even if a specific TSD cannot be confirmed, bloodstains can be differentiated on the scale of hours, days, weeks or years, which is extremely helpful for investigators, particular in reconstructing crime scenes.

Can the method be adapted to bodily fluids other than blood, which may be present at crime scenes?

Yes, our methodology can easily be applied to bodily fluids other than blood. In fact, we have already demonstrated the effectiveness of Raman spectroscopy, coupled with multivariate statistical analysis (or chemometrics), for the identification and differentiation of human peripheral blood, menstrual blood, saliva, semen, sweat, and vaginal fluid. Work on estimating the TSD of other bodily fluids, in a similar way as we have demonstrated for blood, is currently underway in our laboratory.

What challenges need to be overcome before a handheld Raman instrument becomes commonplace in law enforcement agencies?

We have developed our method for “pure” bodily fluid stains on a noninterfering substrate. We are working now on translating the technology to biological stains on common substrates. Some additional challenges for transferring our current technology to a handheld Raman instrument include the relatively high cost of the handheld instruments, and accounting for a low spatial and spectral resolution of handheld Raman instruments relative to the research-grade benchtop Raman microspectrometer used to develop the methodology thus far. We will also need to validate the technique with an accredited forensic laboratory, particularly by analysing real-world or mock crime scene evidence. Although they present real challenges, these factors should not be overall limiting in transferring our innovative technology to a handheld instrument. The cost of handheld instruments continues to decrease as more and more companies begin to release them. We believe that the difference in resolution can be accounted for quite easily, starting with the analysis of bodily fluid stains using a handheld Raman instrument and incorporating those spectra into our existing datasets, and following that up with some advanced data processing techniques. Currently, we have a very good relationship with the New York State Police Crime Laboratory, which is located across the street from the University at Albany campus.

What difference do you think a tool such as this will make to criminal investigations?

We are certain that this tool could have a significant positive impact on criminal investigations. Primarily, if our technology was incorporated for use directly at a crime scene with a handheld Raman instrument, we would be able to assist in the identification of all major bodily fluids (i.e., blood, saliva, semen, sweat, and vaginal fluid). This advantage is two-fold: first, we could confirm whether or not a discovered stain is a bodily fluid (and what bodily fluid it is), and, secondly, by doing this, the number of samples collected and sent back to the lab for further analysis would be drastically reduced. This would cut down on overall costs, potential errors in evidence collection/processing, contamination, and lapses in the chain of custody. Also, having less samples to analyze would help to reduce the significant backlog that most crime labs are currently burdened with. Equally as important, since our technique is non-destructive, any sample that is analyzed will not be altered/affected and would be preserved for subsequent analyses, such as obtaining a DNA profile.

Professor Lednev, Kyle Doty and Mike Nolan were speaking to Anna MacDonald, Editor for Technology Networks.