A pathologist has told an inquest he could not say how a man, found in Swansea's River Tawe two weeks after going missing, died.
Mr Lucas had been on a night out with friends in Swansea
Craig Lucas, 21, from Llanelli, was last seen after being asked to leave a nightclub in March 2003 because he appeared drunk, the hearing was told.
There were no signs he had been injured or attacked and police said how he ended up in the water was a mystery.
His parents have campaigned for more safety railings in the maritime area.
Home Office pathologist Stephan Leadbetter told the hearing at Swansea's County Hall that when Mr Lucas' body was recovered it was consistent with someone having been in the water for up to two weeks.
He said the medical cause of death was unacertained.
"It is not uncommon when bodies are recovered from water for a pathologist to be unable to give cause of death," he said.
Toxicology reports showed Mr Lucas had a blood alcohol level roughly two and half times the legal drink drive limit but the figure may have been distorted by decomposition.
Mr Lucas who worked as a paralegal for the Swansea-based law firm John Collins had gone to a leaving party with around 20 colleagues on 28 March 2003.
They had visited several pubs and a restaurant in the Wind Street area of the city before going to the Revolution nightclub.
Senior doorman at the time Christopher Williams said shortly after midnight Mr Lucas was asked to leave.
"He was a bit unsteady on his feet but he left without argument," he added.
Mr Lucas was last seen crossing a main road heading in the direction of the maritime quarter.
The Coventry University graduate was reported missing by his parents Charlotte and Malcolm as he had failed to return home.
As part of the investigation police divers spent three days searching the marina and lower river Tawe without success.
His body was spotted by a passerby in the water near the Sainsbury store on 12 April.
Despite reviewing CCTV footage from cameras in the area, no trace of Mr Lucas was picked up.
Sergeant Tony Meyrrick said: "Exactly how Craig came to fall into the water remains a mystery."
His parents Charlotte and Malcolm have since campaigned for more safety railings at the waterfront.
A 29,000 signature petition backing the call was handed in to the council.
In 2004 Swansea Council agreed to spend £310,000 on a rolling programme to replace railings in the marina and to investigate whether additional fencing was needed.
The hearing continues on Wednesday.