Snowtown ‘bodies-in-the-barrels’ accomplice Mark Ray Haydon due for release in May | South Australia

A man imprisoned for his involvement the Snowtown murders, one of Australia’s most notorious crimes, could be free within months.

Mark Ray Haydon was convicted for his role in the so-called “bodies in the barrels” murders in Snowtown, South Australia, in the 1990s. Eight of the 11 people killed were found in barrels in a disused bank vault in the town, which is 150km north of Adelaide. A 12th death was linked to the killers.

The ABC reported on Monday morning that Haydon – one of the four convicted over the murders – will complete his 25-year sentence in May.

Haydon was not convicted of murder but of helping to cover up seven of the killings.

The South Australian government said it was “seeking legal advice” on whether newly introduced laws could be used to keep Haydon in jail.

The other three people convicted over the crimes were John Justin Bunting, Robert Joe Wagner and James Spyridon Vlassakis. One of the victims was Haydon’s wife, Elizabeth Haydon.

The SA victims of crime commissioner, Sarah Quick, told the ABC she was in regular contact with the victims’ relatives, who continued to suffer “unimaginable trauma”.

“Contemplating the fact that Haydon will be released is very difficult for them,” she said. “It’s really difficult to reconcile the fact that Haydon might have the opportunity to start a fresh life and that’s certainly something they don’t have the luxury of.”

A SA government spokesperson said authorities were seeking legal advice over a new piece of legislation that criminalises concealing or interfering with human remains.

“This [legislation] delivered on an election commitment that recognised the lasting harm that these despicable acts inflict,” the spokesperson said. “The safety of the community and securing justice for victims are key priorities of the state government.”

The bodies were found when police investigating a missing person case broke into the vault and were faced with a stench coming from barrels filled with hydrochloric acid and the dismembered bodies of eight people.

Investigators initially thought the men’s motive was to take the welfare payments of their victims but a more complicated picture gradually emerged.

It was claimed that Bunting was the ringleader, and that he hated and had targeted homosexuals, paedophiles, overweight people and people with intellectual disabilities. The murders were “often ritualistic and humiliating”.

Bunting was found guilty of 11 murders, and Wagner of 10. Vlassakis pleaded guilty to four murders.

The Snowtown murders fed into a misplaced idea that Adelaide was Australia’s “murder capital”.