Police said they expected the murder toll could rise to 11, as they had yet to account for two missing people who had been expected to have been among the victims.
Police found eight bodies last Friday in a disused former bank vault in the remote settlement of Snowtown, 93 miles north of Adelaide. The ninth body was found buried in the back garden of a house in Adelaide's northern suburbs.
Police announced the formation of a special task force to investigate the killings after results of forensic tests confirmed the number of bodies in Snowtown. The eight bodies were found in a state of advanced decomposition in large plastic barrels, which appeared to have been filled with acid.
Robert Joe Wagner, 27, John Justin Bunting, 32, and Mark Ray Haydon, 40, appeared in an Adelaide court last Fridaycharged with murder. They were remanded in custody until a court appearance on 2 July.
One of the bodies found in the barrels is believed to be Haydon's wife, Elizabeth, 37, who vanished from a northern Adelaide suburb late last year. It was her disappearance that triggered the investigation.
The acting state police commissioner, Neil McKenzie, described the case at a news conference as one of the most challenging in South Australian history. There is no obvious motive for the killings, although there is speculation that the suspects and their victims were all involved in a social security fraud. An earlier theory held that the murders were connected to a paedophile ring.
Detective Superintendent Paul Schramm said the killings did not appear to be random but occurred within a group that had "preyed upon itself".
The task force of 33 officers includes detectives, specialist missing person investigators and crime scene experts. Investigators will use the FBI's violent criminal apprehension programme database to compare aspects of the crime with patterns and "signatures" from other serial killings, police said.
Police believe the murders took place somewhere else and that the bodies were moved to the former bank, which has recently been used to sell plants and arts and crafts.
"They were murdered elsewhere and the [acid vat] drums were brought to Snowtown because it was a quiet little town and there was a premises ideal for the persons involved," a police spokesman said.
Snowtown residents have complained "ghoulish tourists" have already started driving through the town after the publicity over the murders.
Australia's two worst convicted serial killers are James Miller, who raped and murdered seven women in the Seventies, and Ivan Milat, the notorious "backpack" murderer, who killed seven tourists and buried their bodies in the bush outside Sydney in 1989-92.Reuse content