Scientists say cats may be harboring DNA from the crime scene

Ever feel like your cat knows a little more than she’s letting on? Well, maybe you’ve stumbled upon something. New research suggests our little feline friends could be surprising sources of evidence when a crime has been committed.

A cat’s fur, in particular, can contain enough DNA shed by a person who has been close to it to serve as evidence of a fleeting meeting between the two. This could mean that while cats cannot be questioned, they can still help identify abusers.

The new study is the first to look at how pets can contribute to DNA transfer, so there’s still work to be done. But it does represent a positive step towards the future collection of more comprehensive forensic evidence – which of course would be very helpful in police investigations.

“Human DNA collection must become very important when investigating crime scenes, but data on domestic animals such as cats and dogs in their relationship to human DNA transfer is lacking,” says forensic scientist Heidi Monkman of Flinders University in Australia.

“These companion animals can be very important in assessing the presence and activities of members of the household or any recent visitors to the scene.”

In recent years, DNA analysis technology has matured to such an extent that even the smallest traces of genetic material can be relevant to a crime scene investigation. And we messy humans leave our DNA everywhere. Even brief contact with an object can transmit traces of our genetic material. So-called touch DNA alone isn’t enough to positively identify a suspect, but it can be used to support other lines of evidence or exclude individuals.

Touch DNA obtained from a surface does not even require that the person necessarily touch that surface. It can be transported in a number of ways, for example in skin cells or hair floating from a passing body. This is where pets can play a role.

So Monkman and her colleague Mariya Goray from Flinders University, an experienced crime scene investigator, teamed up with forensic scientist Roland van Oorschot from the Victoria Police Forensic Services Department in Australia to see if they could extract traces of readable human DNA from domestic cats could.

Their study was conducted on 20 cats from 15 households. At the study participants’ homes, the researchers wiped the fur on the right side of each cat twice and collected DNA samples from most of the human study participants (one was an underage child from whom no samples were taken). The cat swabs and human DNA samples were then processed.

In addition, household residents completed questionnaires about the cats’ daily behavior and habits. This included how often the cat was touched and by whom in the household.

Detectable amounts of DNA were found in 80 percent of cat swab samples. In all cats, there was no significant difference between the amount of DNA present and the time since last human contact or the cat’s hair length.

The team was able to create DNA profiles by 70 percent of the cats in the study that could be interpreted well enough to be associated with a human. Most of the DNA came from humans in the cat’s own household, but only unknown human DNA was detected in six of the cats.

Two of those cats spent a lot of time in the bed of the child whose DNA was not taken, which could explain some of the “mysterious” results. The origin of the unidentified DNA from the four remaining cats is unknown. None of the households had had visitors for at least two days before the swabs were taken.

One case was particularly interesting: a two-cat, two-person household. One of the cats, a hairless Sphynx, carried the DNA of an unknown third human. The other cat, a short-haired ragdoll, didn’t. Both cats had interacted with each other equally with the people in your household.

Possible sources could be the direct transport of the DNA from a human, for example by petting or by the cat brushing a contaminated surface. The DNA could also have been left behind since the cat’s last contact with a visitor.

“The mode of transmission of this DNA to the cat and its persistence in them is unknown,” the researchers write.

“Further research is needed on the transfer of human DNA to and from cats and the persistence of human DNA in cats and what may influence the different levels of DNA in cats, such as B. Behavioral habits and eliminator status of owners.”

Or maybe the cat wants you to think that…

The research was published in Forensic Science International: Genetics Supplement Series.