A severely decomposed body has been discovered near a walking track south of Adelaide, prompting a murder investigation.

A member of the public made the grim discovery down an embankment of the South Alma walking track at Inman Valley on South Australia's Fleurieu Peninsula on Friday night.

Major crime detectives and forensic officers spent the night at the scene and returned on Saturday to conduct further searches.

Initial investigations confirmed the body had been there for some time.

Mystery surrounds the identity of the deceased and how they died.

Homicide detectives are examining multiple lines of inquiry.

'The remains are very decomposed, they have likely been in this location for several years,' Detective Inspector Andrew Macrae told reporters.

'The circumstances in which we found it make us very confident that the person was unfortunately murdered.'

The body will undergo forensic testing and examination. 

One line of inquiry is whether it has any links to the alleged drug‑related murders of Trevor King, Robert Atkins and Jeff Mundy in Adelaide's southern suburbs.

Mr Mundy was last seen in December 2020 at Seaford, 40km from where the decomposed body was found.

Police have long suspected that the single father was murdered and his body disposed of on the Fleurieu Peninsula.

Police previously believed that Mr Mundy was held captive before his death and that multiple people were involved. His body has never been found.

The body of Mr King, 41, was found at West Lakes in January 2020.

The remains of Mr Atkins, 31, were found in 2023, in a well at an abandoned rural property in the SA's Mid North.

'Because of the geography, it is one of the considerations we will be looking at,' Detective Insp Macrae said.

'Any long-term missing person will be assessed against what we found today.'

Anyone with information is urged to call Crime Stoppers.