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How Cat Hairs Crack Stubborn Crime Cases

Look what the cat dragged in. Few people knew about a British university’s cat DNA database until it helped convict a man of manslaughter.

Last July, cat hairs were found on a curtain wrapped around a dismembered torso that washed up in Portsmouth, England. The Hampshire police sent the hairs to The Veterinary Genetics Laboratory at the University of California, Davis. Because the genetic material could be shared among a number of animals, the scientists couldn’t assess the significance of the DNA match that they discovered between the hair at the crime scene and the hair of the suspect’s cat, “Tinker.”

“We had to keep some details of our database quiet until the case was heard in court,” says genetics researcher Jon Wetton of the University of Leicester. Through the database, the researchers were able to show that only two percent of the U.K. database sample matched the hairs on the curtain—which helped to support the prosecution’s claim of a link to Tinker. Last week, his owner was sentenced to life in prison, with a minimum of 12 years before being eligible for parole.

“With the success of the case, the University put out a press release,” says Wetton. “We thought it would make the inside page of the local paper but it seems to have gone a bit global really.” The international press has exploded with stories about the database.

Could our pets implicate more wrongdoers? Although DNA from human bone, hair, saliva, and blood have revealed the perpetrator in crime scene investigations, this was the first time feline hair was used in a criminal trial in the U.K.

I spoke with Wetton and doctoral student Barbara Ottolini who worked to create the database, which may lead some criminals to avoid brushes with our furry friends.

How did the cat DNA database come about?

JW: We were contacted in April of this year by the Hampshire police because of this murder case. The database was made specifically for the case, but with the intention it would also be useful for future investigations across the country. The funding came from the Hampshire police and was indirectly supported by the Leverhulme Trust.

What kind of information can be gained by such a repository?

JW: We are not looking to identify a specific cat. Mitochondrial DNA types are shared between breeds and every cat who shares the same maternal lineage has the same mitochondrial profile. You can’t with any certainty say ‘I think this came from a Persian,’ for example. The database is specifically for saying whether a particular profile is common or rare. We have hair at the crime scene and we have a cat that we think left hair behind. What’s the chance they match?

What is the database’s main function?

JW: The most likely use is cold cases, when all other lines of inquiry have been exhausted, or to provide additional support with other evidence. We are aware of some very famous cases within the UK where among the evidence, pet hairs were found. No one was able to progress with those at the time. But we need to know which cat is believed to have left the hairs behind—we need hairs or a blood sample from that cat.

BO: Also, if there were a dedicated database in each country, then the investigative power of this technique would increase dramatically.

What’s the chance your pet could help incriminate someone?

JW: In the UK, there are about 10 million cats and 10 million dogs. If you’re a pet owner, you’ll appreciate that your clothes, furniture, and certain parts of the house are pretty much saturated with pet hairs. If someone broke into your house and brushed against curtains as they came in through the window, they might pick up cat and dog hairs. They would end up being tagged by the pet in your house.

How big is the database?

JW: It’s very important for the case that we have the most robust data set possible. We have samples of mitochondrial DNA from 152 cats. We looked at 32 local cats from the immediate area of where the body was found, and 120 samples across the rest of England. We looked at how often we saw Tinker’s profile and it was seen just three times in our database.

Where did the cat samples come from?

BO: They came from pet clinics across the country when cats were taken in by their owners for routine blood testing.

JW: The vet did their tests, and they would have just thrown away the blood samples. We just said, “Can we have any leftover samples from the places we’re interested in?”

Jon, didn’t you set up a database for dogs too?

JW: In my previous job at the Forensic Science Service, we set up a similar database for a similar purpose, working out the likelihood that dog hairs at crime scenes were linked with particular individuals. There was everything from human murder cases where people set dogs on individuals to dog fighting.

How would you distinguish between a cat hair and a dog hair?

JW: It’s difficult. People with a lot of experience can tell them apart under a microscope. You can also test any sample and figure out which species it came from.

How much genetic variation is there among cats? How does that compare to humans?

JW: A lot less than humans and less than dogs as well. When cats were domesticated, only a handful of cats contributed to subsequent generations, creating a population bottleneck. Most variation was lost because virtually every cat these days is probably related to about a dozen founder female cats.

Could the database be used by conservationists to help endangered species, like the tiger?

JW: I would love to do that, and at the Forensic Science Service we developed techniques to look at that problem. One of the main reasons why tigers are in danger of going extinct is because most of the body can be used in traditional Chinese medicine. We set up a test that would allow us to tell if any confiscated medicine contained tiger parts. We are quite keen on looking at our database to see if we can tie it into rare and endangered species.

What would you like to do next?

JW: We’re interested in seeing how much more information we can get from DNA. We’re looking at potentially using more advanced technologies that might hint at breed or hair colors. It’s a pretty major task. You’re not going to be able to do it with a single hair, not for a while at least. Once identifying skin, hair and eye color is worked out in humans, it will be less difficult to do in cats.

Last, but not least. How do people react when you say what you’ve been working on?

BO: They immediately ask whether or not I’ve been at the crime scene. Or they start asking about whether I can clone someone.

Follow Sasha Ingber on Twitter @SashaIngber