Forensic experts hot on the trail of family crime connections

A specialised DNA search that can find criminals via their relatives brought a notorious Adelaide rapist to justice — and signalled a new era in SA for the evolving crimefighting weapon. Miles Kemp reports

The long arm of DNA law is getting longer and catching more criminals in its grasp.

The thinking South Australian criminal must now not only consider if his or her DNA is in the system for crime-scene comparisons but also whether any of their family’s genetic blueprint is there as well.

Forensic Science SA — the low-key, real-life equivalent of the US TV franchise CSI — has revealed how it took an unidentifiable DNA sample from a rape scene and achieved the seemingly impossible: a criminal conviction.

Australia has been slow to catch on to the “familial DNA searching” technique, which for the last 15 years has allowed global law enforcement to narrow down a list of suspects to a single, genetically connected family group.

The lag period ended abruptly in December 2017 when a 12-year prison sentence ended the terror caused by North Adelaide rapist Patrick Mark Perkins.

There had been no leads in the case until 2015. Perkins’ DNA was not on the national database. There was no way to link him to the crime, even if investigators knew who “he” was.

But using a pioneering strategy, Forensic Science SA found another way to tie him to the scene.

The DNA profile the unknown rapist left at the crime scene was a match on the database with someone who must be either their parent or child. The guilty man’s family had let him down — or their DNA had.

The identity of the relative and investigation of the family led police directly to Perkins as a suspect.

Patrick Mark Perkins. Picture: Supplied

Describing the case in a report for other experts, a team of forensic specialists from Forensic Science SA, Flinders University and SAPOL have for the first time described how family DNA matching broke open the Perkins case.

“DNA is passed down from parents to children and therefore it is more likely that closely related individuals will have shared aspects in their DNA profiles than those who are unrelated,’’ the report explains.

“Police generated a list of relatives of the individual identified by the search.

“One individual could be placed in the area around the time the incidents occurred and this person had a similar appearance to the identikit picture developed from the victims’ description of the attacker.’’ Faced with the evidence, Perkins pleaded guilty to the rape. He was jailed in 2017 for attacks on two women.

That success has prompted the forensic experts to seek greater powers to use their new tools.

As with many breakthroughs which have the potential to infringe human rights, authorities have been cautious about how and when the family searches can be done. For example, familial searches overseas have even used DNA databases constructed for genealogy research, but not yet in Australia.

In publishing their success story in the Australian Journal of Forensic Sciences this month, the SA experts have called for far wider powers than currently exist, which is likely to be met with caution by politicians. “Currently in South Australia, familial searching is governed by policy which puts strict limitations over what circumstances a familial search can be undertaken,’’ the report finds.

“This limits searches to only the most serious of crimes and only after extensive investigation has been undertaken to exhaust traditional policing avenues.

“Consideration should be given to performing familial searching much earlier in serious crimes to minimise the expensive and time consuming police investigation currently required to be demonstrated for a search to be considered.

“If familial searching is an extension of direct database searching, then this would seem like a logical path forward in order to reduce costs and bring cases to resolution, potentially years earlier.’’

A women walking along the street in North Adelaide.

Other DNA breakthroughs are occurring in SA, although at an individual level they cannot yet boast the headline-grabbing success of the North Adelaide rapist case.

Along with SAPOL’s extraordinary recent success in cold case crime-solving, forensic experts are doing their part in solving the seemingly unsolvable. Software as well as policy and DNA science is also leading to breakthroughs, says Forensic Science SA’s Tegan Collins.

She has studied the impact of two new technology breakthroughs in SA on providing better evidence to police in so-called “no suspect cases’’, in problematic investigations when numerous DNA samples are mixed together from a crime scene.

“Data from our no suspect workflow was collected for a 10-month period from September 2017 to June 2018,’’ Ms Collins said. Her study using these cases shows that two new developments at Forensic Science SA have significantly improved information supplied to the police.

“Mixture searching” in DNA matching has long been difficult because of the presence of two or more donors to the sample, she says.

“Our STRmix program is now able to compare a database of reference DNA profiles against mixed DNA profiles obtained from crime scenes,’’ Ms Collins explains.

“During the study period, there were 53 mixed DNA profiles searched, and 42 additional new links in 35 cases were provided to SAPOL. “The overall match rate for mixture searches was 79 per cent.’’

Ms Collins says better technology has also been able to get more SA information onto the National Criminal Investigation DNA Database.

“Overall with the two improvements over the time of the study, we provided an additional 68 links, which is an increase of 13 per cent over the standard in no suspect cases,’’ she says. National improvements mean family DNA matching is also set to take off as a police tool in Australia.

New software used by the National Criminal Investigative DNA Database promises to make family searches more co-ordinated and standardised including those in SA.

With national co-ordination for the first time criminals will have to worry that the DNA of a wayward relative is on file, even if they are in another state or territory.