Police believe the body of a man found in a well in Surrey had been there for about two years before it was discovered last week.
Detectives also say the man had been assaulted and tied up and the incident is being treated as murder.
The body was discovered by workmen at an address in Audley Drive, Warlingham, on Friday.
Seven men aged between 21 and 27 arrested on suspicion of murder have been bailed to a date in late December, pending further investigation.
The seven men, all eastern European, worked at a car wash very close to the well, Sky News has learned.
The manager of the garage has said that the arrested men all worked at his car wash.
But he said some of them had only been in the UK for a few months and therefore were not around two years ago when police believe body was dumped.
A post-mortem on Sunday did not discover a cause of death, and further tests are being carried out.
But it did reveal that the body, confirmed as that of a white man, had injuries consistent with an assault before it was bound up and placed in the well, Scotland Yard said.
Detective Chief Inspector Cliff Lyons said officers were reviewing missing person reports to try to establish the man's identity.
"Given the complex nature of this investigation, it is likely that forensic work at the property will continue for a further month as we attempt to secure all available evidence," he said.
"While our work continues to establish the facts of how this male came to sustain his injuries and his body end up in the well, our focus is also on finding out his identity.
"This is someone's son and my team owe it to him and his family to find out the truth and bring those who committed this atrocious act to justice."
