Welsh police used fingerprints from a WhatsApp photo to nab a drug dealer

Alan Martin April 17, 2018

Some time ago, cybersecurity experts were warning that smartphone photographs were now of a high enough quality that criminals could potentially lift fingerprints from a peace sign and unlock a smartphone with them. Well, now the shoe is on the other foot (or more accurately: the glove is on the other hand) as police in South Wales have used a grainy WhatsApp photograph of a hand holding ecstasy tablets to successfully arrest a drug dealer.

Welsh police used fingerprints from a WhatsApp photo to nab a drug dealer

With WhatsApp using end-to-end encryption, this wasn’t a case of intercepting a message – rather South Wales Police found the photograph on the phone of someone arrested in Bridgend. “It had a number of texts such as ‘what do you want to buy?’ on it,” Dave Thomas from the South Wales Police scientific support unit told the BBC.

“There was then the photograph of the hand holding pills that seemed like it was sent to potential customers saying ‘these are my wares, I’m selling these’. But he was not thinking it showed part of his hand and there was potentially a fingerprint.”

That doesn’t quite tell the full story – the picture in question on the BBC website is pretty low quality, and the top of the finger is covered, which is unfortunate, as that’s the part kept on national fingerprint databases. As such, there was no match, but there was enough corroborating evidence for the police to have a suspect in mind, and upon raiding the house and comparing again, they believe they have the right man: “While the scale and quality of the photograph proved a challenge, the small bits were enough to prove he was the dealer.”

Beyond reasonable doubt?

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If that makes you feel a little uneasy, it’s with very good reason. Although we’re taught to believe that fingerprints are unique, we just don’t know that for sure. And while in this case the corroborating evidence proved decisive, that’s not entirely reassuring as a precedent for less clear-cut cases given that contextual bias has been shown to influence fingerprint examiners. Plus, as Gizmodo points out, a 2011 study found that even in perfect lab conditions, mistakes can be made: from 169 fingerprint examiners, 3% made a false positive and 85% made a false negative.

And to be clear, this case was far from perfect lab conditions: I’ve already linked to the photograph in question, but it’s worth having another look with the paragraph above freshly in mind.

Still, South Wales police is feeling flush with this victory, and Thomas is keen to see if further cases can be cracked in this manner: “It has now opened the floodgates and when there is part of a hand on a photograph, officers are sending them in.”

And that’s just the beginning. “We want to be in a position where there is a burglary at 20:30, we can scan evidence and by 20:45 be waiting at the offender’s front door and arrest them arriving home with the swag,” he added.

An important first step to that plan might involve not tipping off criminals by telling the UK’s most-read news site that you’re now looking at seized phones for photographs of fingerprints, of course. Gloves are a cheap and low-tech form of security, but they certainly do the job, as burglars have found for decades.