Researchers at the University of Leicester in England have found a new way to link suspects to a crime scene or a victim using cat hair DNA. They say that a single strand of cat hair left at a crime scene can be linked to an individual cat — provided there was a cat.
Conversely, if the suspect has a cat, they may also leave tell-tale traces of their cat’s hair at the scene, which can be a foolproof way of linking them to the crime scene.
But we know DNA profiling or trace DNA has existed for over 30 years, so why haven’t forensic investigators used pet hair DNA before?
Why it has been challenging to use cat hair DNA in criminal cases
Investigators have always known that pet hair can offer vital clues. But even with the latest technological advances, it’s been challenging to zero in on an individual cat using cat hair DNA.
Usually, the root of the cat’s hair dries up when it is collected for evidence. The root contains nuclear DNA, which can be used in forensic investigations because it has clear, repeated stretches of genetic code called short tandem repeats (STR). So human hair has always been more viable than cat (pet) hair because the hair a suspect leaves at a crime scene usually has hair roots.
“Hair shed by your cat lacks the hair root, so it contains very little useable DNA,” said Emily Patterson, a Leicester Ph.D. student and the lead author of this study. “In practice, we can only analyze mitochondrial DNA, passed from mothers to their offspring and shared among maternally related cats.”
She means that even with the mitochondrial DNA, it would be challenging to match it to an individual cat because this DNA is usually broken into fragments in the cat’s hair, leading to an incomplete DNA reading. Also, pet cats come from a few ancestors, and a hair sample from a crime scene may match thousands of cats.
The scientific breakthrough that could use cat hair DNA to catch criminals
As mentioned, matching cat hair DNA samples to a specific cat has not been easy. However, Patterson and her team have revolutionized DNA reading by increasing “the detail with which they can analyze the mitochondrial DNA.”
With these advancements, forensic investigators can now use fragments of a cat’s mitochondrial DNA to make billions of copies. Each fragment copy has the same genetic code from the cat’s mitochondrial DNA. Still, every copy acts as a piece of a larger puzzle.
Previously, technology may have struggled with a few copies, but when you have billions of copies, it can see the genetic code the fragments have in common. So you can recreate the complete mitochondrial DNA of a cat and know which cat a hair strand belongs to.
Real-life use of cat hair DNA evidence
Cat hair DNA analysis in 2013 helped solve a homicide case. In this case, prosecutors in Britain linked the DNA from the suspect’s pet’s hairs to those the suspect had left at the crime scene. However, this case relied on an earlier DNA analysis technique, but with the new developments, investigators can rely on something other than luck.
“In a previous murder case, we applied the earlier technique, but were fortunate that the suspect’s cat had an uncommon mitochondrial variant, as most cat lineages couldn’t be distinguished from each other,” said Dr. Jon Wetton from the University’s Department of Genetics & Genome Biology, who co-led the study. “But with our new approach, virtually every cat has a rare DNA type, so the test will almost certainly be informative if hairs are found.”
This new technique was used in a case involving cat cases effectiveness. The researchers used DNA from the lost cat’s skeletal remains and successfully matched it to a strand of hair from its surviving male offspring.
Today, suspects may painstakingly try not to leave their DNA behind. But our feline friends shed thousands of hairs and may be a valuable source of forensic DNA.
“In criminal cases where no human DNA is available to test, pet hair is a valuable source of linking evidence, and our method makes it much more powerful. The same approach could also be applied to other species — specifically, dogs,” added Mark Jobling, professor of genetics and the study co-lead.
