The family of a missing bank worker have called for anyone with information to help end their "relentless nightmare" as a €100,000 reward is offered to solve the case.
Trevor Deely was 22 when he vanished in south Dublin after calling to his office in the then Bank of Ireland Asset Management building on Wilton Terrace early on December 8 2000 following a work Christmas party.
New enhanced CCTV footage shows a man in black clothing acting suspiciously at the rear entrance to Mr Deely's office block between 3am and 3.34am, just before Mr Deely arrived.
His sister Michele Deely said bringing Trevor home would mean the world to the family.
"As a family, we have never believed that people can disappear into thin air," she said.
"We know someone knows something. We ask that you come forward and put an end to this relentless nightmare.
"Many people have over the past 16 years have questioned why we continue to search for Trevor. The answer is simple if you knew Trevor. It can be summed up by saying if the situation was reversed he would never give up on us."
Gardaí in a cold case unit discovered an old VHS CCTV recording which was digitally enhanced by experts in the UK.
It shows the man dressed in black step out on to the footpath outside the offices on Wilton Terrace, a short distance from Baggot Street bridge, at 3.34am.
Moments later, Mr Deely can be seen arriving at the rear gates of the bank offices followed by the man and the two of them have a brief conversation.
Mr Deely leaves through the same gates carrying an umbrella and stops briefly to fix his jacket.
The last sighting of Mr Deely is on CCTV as he passes a Bank of Ireland ATM machine on Haddington Road at approximately 4.14am.
Gardaí believe that the man who was filmed acting suspiciously outside Mr Deely's workplace is seen walking the same direction down Haddington Road 34 seconds later.
The case has remained among the most high-profile missing persons investigations in Ireland.
Tim Dalton, chairman of Crimestoppers, revealed an anonymous donor has put up a €100,000 reward for information which "might prove critical in resolving the case".
"It is not Crimestopper money, because we don't have that kind of money," he said.
"We do make awards sometimes, but never of that amount. This a private donation."
Detective Superintendent Peter O' Boyle, of the cold case unit which took on the missing persons case in 2016, said it has 172 statements in relation to the investigation and re-interviewed almost all those who have come forward in the past.
The man dressed in black in the CCTV footage has not contacted gardaí.
"He's one of the people who spoke to Trevor on the night. We are not focusing our inquiries specifically on one line. It's one that we would like to bring to a conclusion," he said.
The Deely family, including his father Michael, brother Mark, and sisters Pamela and Michele, joined detectives from the cold case unit and Crimestoppers to publicise the latest appeal.
They also took to the streets around Baggot Street bridge at lunchtime, including Haddington Road where Mr Deely was last seen, to hand out leaflets to workers and passers-by in the hope of finding new information.
Posters about the case have regularly been posted on lamp-posts in the area in the 16 years since he disappeared.
