Forensic science researcher Sally Kelty said the case is the first in Australia - and possibly the first ever - in which investigators have used DNA extracted from a bloodsucker like a leech or a mosquito to solve a crime.
"It's certainly unique and shows how the boundaries of DNA technology have been pushed since it was first introduced to Australia 22 years ago," the University of Tasmania state researcher said.
The leech dropped off Peter Cannon as he and an accomplice tied a 71-year-old woman to a chair in her remote home in the Tasmanian woods on Sept. 28, 2001, and stole several hundred dollars in cash, police said.
Detectives found the leech at the crime scene and extracted blood from it that they believed was from one of the two suspects.
They identified Cannon as that culprit when he was arrested last year on unrelated drug charges and authorities for the first time recorded his DNA profile.
Cannon, now 54, pleaded guilty in the Tasmanian Supreme Court on Monday to aggravated armed robbery. He will be sentenced on Friday and faces a possible maximum of 21 years in prison.
Detective Insp. Mick Johnston, who was involved in the police investigation from the outset, said the leech was the only forensic evidence found at the crime scene.
He said he was happy with the guilty plea, especially for the victim, Fay Olson.
"She's waited a long time for closure to this matter and it's nice to be able to deliver that," Johnson told Australian Broadcasting Corp. radio.
Police are still searching for Cannon's alleged accomplice.