Foul play cannot be ruled out in the disappearance of a man from a North Sea ferry 40 years ago, police have said.
Kevin Dundon, from Essex, was 22 when he went missing while on a vessel returning to Felixstowe from Zeebrugge in Belgium, on 21 September 1980.
The ferry was off the Suffolk coast when the kitchen worker was last seen.
His body was never found and police reviewing the case said there was "growing support to suggest Kevin's disappearance was not accidental".
Suffolk Police said no evidence as to what happened to Kevin was ever found, and his status has remained as "missing" for four decades.
'Torn apart with grief'
"Over the last two years we have identified and taken statements from individuals who were not seen at the time, but were on board the Viking Viscount with Kevin," said Andy Guy, the Major Crime Review and Unsolved Case Manager for Norfolk and Suffolk Constabularies.
"There seems to be growing support to suggest Kevin's disappearance was not accidental."
Mr Dundon's brothers said in a statement they believed it was "extremely unlikely Kevin could have gone overboard without being seen" and said "seeing our family being torn apart with grief was virtually unbearable".
Mr Dundon, from Clacton-on-Sea, was employed by shipping company Townsend Thoresen and had been working on to the Viking Viscount for just three days when he disappeared.
His duties included washing crockery in the galley. Witness statements from colleagues said he was working in the plate room at about 18:00 BST that Sunday, and the last confirmed sighting of him was 30 minutes later when he is believed to have been seen exiting the galley through a door which could have taken him to either the toilets or the deck.
The ferry was about 26 miles (42km) off the Suffolk coast at that time.
Mr Dundon did not respond to announcements made over the public address system and, when the ferry docked at Felixstowe at 20:45, further searches were carried out on board.
Later that evening the coastguard carried out a "man overboard" search but no trace of Mr Dundon was found.
Mr Guy said: "Forty years have now passed since Kevin Dundon disappeared and his family have been devoid of any explanation as to what happened to him since.
"The original investigation faced some considerable hurdles due to the fact Kevin was on a ferry 26 miles out at sea when he was last seen alive, and which was carrying almost 700 souls."
Some passengers could not be traced as they were travelling on identity cards rather than passports, he added.
Brothers 'deserve answers'
Police said they believed it was "highly unlikely that Kevin was still on the ship when it docked at Felixstowe", and a spokesman said that foul play could not be ruled out.
Appealing for further witnesses, Mr Guy said: "I believe there are individuals who were on that ferry that know what happened to Kevin, but have not previously told us.
"Kevin's parents died without knowing what happened to their son, but there are three brothers who deserve to be given some answers and closure about the fate of their sibling."
In a statement released through police on the 40th anniversary of Mr Dundon's disappearance, his brothers said: "We implore anyone aboard the Viking Viscount that evening who may remember anything - however small - about the incident, to please contact the police.
"It could be that a friend or relative may have mentioned something over the years and it would mean everything for us to finally know what happened to Kevin that evening, and finally give us closure."