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Police use discarded chewing gum to figure out what a suspect looks like
07 Dec 2015

Face-off: Image of 'Serial Creeper'
Face-off: Image of 'Serial Creeper'
Genetic scraps of evidence from material such as chewing gum are helping police to unmask the faces of criminals who their victims have never seen.

Thanks to discarded bits of DNA left behind by suspects, a genetics company is piecing together the digital likenesses of offenders.

Police in Florida have turned to science in the search for a man who has terrorised at least a dozen women over the last two years.

The suspect has been peeping into windows and slipping into bedrooms to watch his victims sleep. He has touched several women’s feet or hair — and some, he has sexually assaulted.

Dubbed the “Serial Creeper,” the Miami police are desperate to find him.

They have released this sketch of a dark-haired, dark-eyed Latino man with smooth skin, high cheekbones and a pointed chin.

But the impression was not drawn by a police artist based on eyewitness accounts. The Creeper has kept his face covered in every assault, Florida police spokesperson Kelly Denham told Science News. “He’s never been seen.”

So local police had to pursue a less-conventional route. They bought a computer-generated image based on the Creeper’s DNA.

They paid genetics company Parabon NanoLads £3,500 to analyse the DNA the Creeper left behind – to “mash-up” a likeness of the Creeper’s face.

The images Parabon create do not offer an exact picture of a suspect, says Ellen Greytak, the company’s bioinformatics director.

“We work with law enforcement agencies to give them an idea of who they should be looking for,” she said — or more especially which people to cross off the suspect list.

This isn't the first time the company has used genetic scraps to create images of stranger's faces.

Back in May, it teamed up with a Hong Kong advertising agency to shame local litter louts for polluting the streets.

Using the DNA left behind on chewing gum and cigarettes, Parabon zeroed-in on genes that code for physical traits like hair and eye colour. Then, they drafted computer-generated sketches of each polluter's face, printed them out on giant wanted posters, and pasted them on billboards throughout the city

The science behind the idea — of using DNA to predict a face — has existed for years.

In 2012, New York City-based artist Heather Dewey-Hagborg used the same technology to make sculptures of complete strangers using only the tiny bits of DNA left on discarded cigarettes and chewing gum that she collected from the streets of New York.

Each piece of rubbish that Ms Dewey-Hagborg collected was rich in genetic data, typically in the form of DNA encased in dried spit or inside pieces of hair and skin.

To isolate that DNA, she conducted a simple laboratory procedure. Then, using a computer programme, she combed through all the DNA and picked out only the genes that code for physical traits, like hair and eye colour.

Her exhibit, called "Stranger Visions," has been shown in galleries across the world.

In addition to hair and eye colour, these bits of our DNA dictate the shade of our skin, the width of our noses and the distance between our eyes, but they cannot tell how old or physically fit a person is.

It is the same rule that applies to the images Parabon create.

As vague as it is, a general idea is all the current science can guarantee. That is because each of us has three billion chemical base pairs of DNA that altogether make us who we are, says Parabon.

One method of analysing all of these genes is looking at evidence linked to specific traits like hair and eye colour, susceptibility to certain diseases, and ancestry. This method of DNA analysis is called SNP (pronounced "snip") sequencing.

The technique is far better at predicting certain traits than others. Scientists can use it to predict blue and brown eye colour and red hair colour, for example, with pretty striking accuracy. But blonde hair is much trickier, and things like height and face shape are another matter entirely.

It’s a hazy place, the scientists agree, where the roots of a person’s looks hide out in their genetic instruction books.

Scientists dig up these roots by linking people’s physical features with tiny landmarks in their DNA. If crime investigators could use DNA to predict nose width, say, or eye size, they might have an easier time identifying criminals.

Parabon has not yet published a study that tests its predictions’ accuracy, but a number of law enforcement agencies have checked it out, says Ms Greytak.

Sometimes agencies give the company a test drive, and send out a few DNA samples before buying the product. The agencies then compare photographs with Parabon’s predictions. “We’ve nailed every single one of those,” she said, though the agencies have not made test results public.

Parabon’s predictions consider genetic information about sex, ancestry and facial characteristics from databases that include about 15,000 people. Still, Ms Greytak says, “we need a lot more data. That’s the big thing.”

If you want to capture the variation of human faces, she says, you need to know what a wide variety of faces look like relative to their genetics.

She acknowledges that Parabon’s technology cannot identify individuals, like a photograph can. But the technology is “absolutely ready from the point of view of exclusion,” she said.

Investigators can use the images to rule out suspects. So in the search for the Serial Creeper, for example, police could eliminate suspects with red hair and blue eyes.

For the Creeper, who has not been linked to a crime since August, the profile gave stumped investigators a new avenue to explore.

“We’re at a standstill in the investigation — that’s why we turned to the Parabon DNA profile,” Ms Denham added. “Let’s see what we can come up with to try and find this person.”


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