Crime scene investigators may have a new method in helping them catch criminals. Scientists from Lawrence Livermore National Laboratory in California found that unique protein markers in a strand of hair could be used alongside DNA profiling to identify humans. Hair protein is more stable than DNA, which breaks down over time. The experts claim that this new method could identify humans up to 250 years after being left behind. Brad Hart, chemist at LLNL and co-author of the paper detailing the research, explains how the new technique works.
How did this research come about?
We have been interested for many years in how we can assist in the development of new science-based approaches to forensics that do not rely on subjective methods. We began working with Dr. Glendon Parker, who originated the concept of using hair proteins in this way. Together we built a team and expanded the research in this area.
What’s the main point of it?
Mutations in DNA can sometimes result in small changes to proteins. We have shown that it is possible to measure those changes in the proteins that make up hair. Since the changes we are looking for are tied to the genetic code we can determine if a hair belongs to a specific person with some level of statistical certainty. This is very important because, while DNA is currently the best way to identify a person with certainty, it is not very stable in the environment and can be very difficult to collect from a crime scene. Proteins, however, are much more stable.
How did you create this new method?
We have developed specialized chemistry to isolate the protein from hair. Then we used a powerful instrument called a mass spectrometer to analyze it and identify the very small variations in the structure. Finally, we trace those variations, or markers, back to the person’s genetic code by analyzing the DNA. We have analyzed hair from over 75 men and women as well as from historic remains which are hundreds of years old. From those samples we have identified well over 100 markers that allow a power of discrimination of around 1 in 100,000. We are working now to increase the number of markers, which will allow much higher specificity to be obtained.
Were you surprised by these results?
We have been somewhat surprised at how specific this method can be for identifying a specific person. This is because we have been able to identify many markers in hair proteins. It has also been exciting to learn of the other applications beyond traditional forensics such as its potential use in archaeology.
What impact could your research have?
Currently there are two forensic tools for human hair. One method is microscopic hair comparison, where hair from a crime scene is compared to hair from a suspect. A trained expert determines if they come from the same individual. This approach is highly subjective and very dependent on the expertise of the examiner. It is also impossible to state with confidence the probability that the hair did or did not come from a specific person.
The second, and more modern, approach is to use DNA. The more powerful nuclear DNA is not present in hair, but another type of it, from structures in the cell called mitochondria, is available and can often be used. However, the specificity that can be obtained with this kind of DNA is much less than what we can achieve using protein. Additionally, DNA eventually breaks down and often it is harder to see in older hair. Our approach looks at the proteins in the hair, which is considerably more stable and lasts well after DNA has disappeared from the sample. We look for protein variation in hair that can be used to predict what was in someone’s DNA, even if it is no longer present in the sample.
Will your method become a game changer in the future?
Yes, we believe so. By developing a science-based method for human identification that does not require the presence of DNA we are providing a completely new tool for the forensic community. Hair is a very common type of evidence. We are trying to unlock its power to help solve crimes.
We are continuing to identify protein markers in hair. The more markers we identify the more powerful the method will be for identifying people. We are also beginning to look at tissues other than hair such as bone, teeth and skin to determine if markers present in those materials can also be used for identification. Finally we are working to make the method work with as small a sample as possible so that this can be used for a wide range of evidence.