Garda∅ in Galway believe the body of a man discovered at the rear of a house in Salthill last week may have been buried in the shallow grave for at least 10 years.
A post mortem carried out by the State Pathologist, Dr John Harbison, failed to reveal the cause of death.
"We have no definite cause of death at this stage and, hopefully, further forensic examinations will throw some light on this in the very near future," a Garda spokesman said.
"We cannot launch a murder investigation until we know how this person met his death. But the circumstances are definitely suspicious," he added.