Marc Renton - another DNA mistake? Qld government must reopen the case

The genetic code of a new human begins when sperm fertilises the ovum of the mother-to-be and forms a brand new cell which carries half the genetic heritage of each parent through structures called chromosomes. The chromosomes comprise a chain-like structure of genes made from DeoxyriboNucleic Acid (DNA) molecules.

Two strands of protein molecules entwine to form the famous double-helix structure of the DNA molecule with all the information needed to build, control and maintain a living organism in chemically coded form.

Genetic profiling or restriction fragment length polymorphism (RFLP) is used to analyse DNA found in biological materials such as blood, semen, bone and hair found at the scene of a crime. A chemical called a restriction enzyme is used to divide the DNA into fragments, which are then separated according to size by another laboratory technique, electrophoresis. The separated fragments form a pattern of parallel bands that reflect the composition of the DNA. In principle, the pattern produced will always be unique to any person. This technique enables scientists to compare two samples, one taken from the crime scene and one taken from the suspect, and determine whether the samples came from the same individual.

It is that unique and individual genetic code that is helping law enforcement solve unsolvable crimes. In the criminal justice system DNA profiling can eliminate suspects as well as enhance the successful prosecution of guilty offenders - but unfortunately DNA profiling is not an infallible tool in the lawyers' arsenal.

1) Charges in the 1997 Arnott's biscuit extortion case were dropped as a result of flawed DNA testing procedures at Queensland's John Tonge Centre.

Tweed Heads great-grandmother, Joy Ellen Thomas, 72, was accused of threatening to poison the company's biscuits unless four Sydney detectives took lie-detector tests concerning evidence they gave against her son, convicted murderer Ronald Henry Thomas. The prosecution against Mrs Thomas relied heavily on evidence from forensic biologist Barry Blair, who conducted DNA testing for the Crown at the John Tonge Centre.

Blair testified that DNA recovered from a stamp on one of the extortion letters matched Mrs Thomas's DNA but the stamp had not been tested for saliva, so it could not be determined whether Mrs Thomas had licked the stamp. Blair claimed that although saliva testing would have identified the source of the cells it would have ruined any chance of recovering the DNA profile.

During the pre-trial hearing on April 24, 2002, Blair changed his opinion about the key DNA evidence after a forensic biologist hired by the defence, Lazlo Szabo, revealed the existence of a second DNA profile from an unknown person also present on the stamp.

Szabo, from Tasmania's Forensic Science Laboratory Centre, believed the presence of the second person's DNA was evident at twice the levels recorded by the Blair. His report detailing the second DNA profile was given to the Crown two months before the pre-trial hearing. Although the presence of the second person's DNA was indicated within a table in Blair's reports, it was not mentioned in the text because, as he testified at the pre-trial hearing, the second profile was a "stutter" - an anomaly in the testing procedures.

The presence of a second DNA profile was evidence that could have freed Mrs Thomas months earlier but the Crown opted to remain silent about its existence until they were forced during the pre-trial hearing to concede the legal significance of two DNA profiles being present. Prosecutor Paul Rutledge argued that the Crown's silence resulted from a difference of opinion between the two experts.

Rutledge, who had successfully prosecuted Ronald Henry Thomas at his 1994 murder trial, withdrew the charges in Brisbane Supreme Court on Friday 26 April 2002.

2) Frank Alan Button, 32, served ten months of a seven-year sentence for the rape of a 13-year-old intellectually impaired girl before independent DNA testing established that he was not the perpetrator of the crime.

The young girl claimed she had been assaulted during a party at her mother's home at Cherbourg, southern Queensland, on February 17, 1999. The following day she told two school friends she might be pregnant because she'd been raped. The school principal called the police and detectives took her back to the house where the rape had occurred.

Frank Button was asleep in a drunken stupor inside the house when police arrived. He became the prime suspect because he was wearing a shirt similar to the one the girl described to the police. Button was taken to the local police station where he was interviewed and subsequently charged with rape and locked up.