Witnesses saw 79-year-old Roy Chalmers seconds before he plunged 150ft down cliffs to his death at Brighton Marina, it has emerged.
The question police now want answered is: Was he alone before he fell?
Detective Chief Inspector Steve Dennis, heading Operation Herne, said: "We know Mr Chalmers died as a result of falling from the cliff but what happened just before is still unknown.
"It may be that Mr Chalmers fell but at this stage we cannot rule out the possibility that there were suspicious circumstances."
He said the witnesses had seen Mr Chalmers, of Overhill Gardens, Patcham, Brighton, at the cliff edge at 8pm.
His body was discovered at Brighton Marina on Friday.
He went missing on Easter Monday after being dropped off by a friend in Marine Gate, opposite the marina.
Mr Chalmers' whereabouts remained a mystery until Southern Water workmen at Brighton Marina made the discovery of his body.
A post-mortem examination showed the cause of death was multiple injuries consistent with a fall.
Police want anyone with information to call the incident room on 0845 6070999.
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