In 2001, an elderly woman in rural Tasmania, Australia's southernmost state, was home alone when two men broke into the house. They tied her up in a chair, poked her with sticks, forced her to open the safe and stole AUS$550 in cash.
Little forensic evidence was found at the scene until one of the detectives noticed an engorged leech next to the chair where the victim had been tied up. None of the detectives or the victim had a leech bite, so it was highly probable that the leech had fallen off one of the offenders—after attaching to him as he made his way to the property through the bush.
Blood from the leech was placed on an FTA® card, as per the standard practice for taking a reference blood sample from a person, and sent to the forensic laboratory for DNA profiling. It was not known at this stage if the technique would work on blood from a leech.
DNA was extracted from the FTA® card using the standard procedure for blood on FTA® cards, which involves washing the disc (first with NaOH, then with a 0.1X Tris/EDTA buffer), then amplified. A full human DNA profile was obtained—presumably from the last person the leech had bitten.
At the time, the profile obtained did not match any profiles on the DNA database and remained on the database as an unsolved crime.
Late in 2008, a man was arrested on drug offences, and a routine DNA sample was collected. When the profile from this sample was searched against the DNA database, a match was found to the profile from the leech.
The man now faced charges of aggravated armed robbery as well as the drug charges. He pleaded guilty to the armed robbery and received a 2-year sentence.
Good lateral thinking by the detective, alert for any potential evidence, combined with the application of standard DNA-profiling techniques to a new situation resulted in a probable world first—a man convicted on the basis of a DNA profile from a leech.
The second offender remains unidentified at this time.