The Silent Witness: DNA from a Leech

Sep 30, 2013 - by Liz Porter - 0 Comments

A forensics first occurred in 2008 in Tasmania when DNA harvested from a leech led police to a robber.

by Liz Porter

On a late spring afternoon in 2001, two intruders broke into a house in bushland outside the small town of Launceston, in the Australian island state of Tasmania.

The men had apparently heard that the place was a soft target: It had a safe, which suggested money, and firearms – and it was occupied by an elderly couple. Donning black hoods and arming themselves with sticks, the men broke in, finding pensioner Fay Olson alone and terrified.

Forcing her to open the safe, the men stole $500 and a further $50 from the 70-year-old’s handbag. Then, grabbing a belt and tracksuit pants, the men tied their victim up and left.

The woman managed to break free and call police, who were on the scene within an hour. The officers were disappointed to hear that Mrs. Olson could give them little in the way of a description of the intruders because their hoods had covered their faces. It seemed unlikely, given the isolated location of the house, that police would find any witnesses who might have spotted the robbers approaching the house.

But one of the police officers present, Senior Constable Nathan Slater, was still able to spot one potential witness. It was small and entirely silent, but potentially very eloquent. It was a fat-bodied leech, its engorged appearance suggesting that it had recently eaten – meaning that it was full of human blood. But whose blood? Neither of the officers on the scene nor the victim had been bitten. So it t seemed safe to assume that the creature had fed on one of the robbers. Then, sated, it had simply dropped to the floor.

The “silent witness” was sent to the state forensic center, and the blood inside it was analyzed. A  DNA profile was extracted and went onto Tasmania’s DNA database.  It didn't match any of the criminals’ profiles already on the base. But the police were happy to wait. They were fairly certain that the leech’s victim would commit other crimes in the future. When he was caught and charged, his DNA would be taken, his profile would go on to the data base – and it would match the profile taken from the leech.

In the meantime the case was not forgotten. Tasmanian forensic scientists often quoted it when reporters asked them if their working life bore any resemblance to the TV show “CSI.”

In 2006 the forensic biologist who had done the DNA extraction – a tricky job because he had to be sure he was getting the human DNA, not the leech DNA – told a reporter about it. By then the scientist was working in another state, and had lost track of the case. “It may have found a match by now,” he told the journalist.

In fact he would have to wait another two years before the sample he had extracted from the leech could fulfill its potential – and make world headlines because the solving of a crime via DNA harvested from a leech would be a forensic world first.

Late in 2008, seven years after he broke into Fay Olsen’s house and robbed her, Peter Alec Cannon, 54, was charged with drug offenses and DNA profiled. His profile matched that of the blood from the leech.

Cannon pleaded guilty to the robbery and was sentenced to two years jail. His co-offender remains at large.

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