One man will be charged with murder and four other people with related offences over the suspected drug-related killing of Adelaide man Robert Atkins.
Police on Wednesday said a 32-year-old man had been arrested and would be charged with murder, unlawful detention and causing harm.
Two other men, aged 32 and 43, and a 25-year-old woman would be charged with unlawful detention and causing harm.
A 33-year-old man would be charged with procuring the unlawful detention of Mr Atkins, who was reported missing in late 2020.
Detective Inspector Brett Featherby said it would be alleged the 29-year-old was assaulted multiple times and held at a number of locations before being taken to SA's mid-north and killed.
His body has not been found.
Insp Featherby said it was hoped Wednesday's arrests would give people with information about his death the confidence to come forward.
"Our priority is to locate Robert's remains and allow him a dignified burial," he said.
"I ask the public if anyone does have information that could lead to the location of Robert's remains to contact us."
The death of Mr Atkins was thought to be linked to the drug trade and prompted police to establish a special task force in late 2021 to investigate his murder and those of two other men, Trevor King and Jeff Mundy.
Mr King, 41, was found dead at suburban West Lakes in January 2020 with police now believing his death was staged to look like a suicide.
In the months before his death, he was the victim of unlawful detention and serious assaults, resulting from a drug debt.
Mr Mundy, 36, was last seen in December 2020. His body has not been found, with police suspecting it was disposed of somewhere on SA's Fleurieu Peninsula.
