How drowning and suicide were dismissed as possible explanations
There were many theories about what could have happened to Trevor Deely.
A CCTV image of a tall and thin man aged 22 carrying an umbrella as he walked at Baggot Street Bridge at 4.14am on December 8, 2000 was the last sighting.
Trevor had called into his workplace at Bank of Ireland Asset Management after leaving a Leeson Street nightclub on the night of the office Christmas party.
It was believed that he was walking home to his flat in Serpentine Avenue, Ballsbridge.
One theory was that after his night out he had fallen into the Grand Canal or the River Dodder on his way home.
It was a very windy night - could a strong gust of wind tugging at the umbrella have caused him to lose his balance and fall into the water?
There was speculation about a possible suicide.
Trevor's sister Michelle was living in London at the time and she made a number of calls to Trevor's phone over the next couple of days before anyone realised that he was missing.
She said she could hear Trevor's phone ringing several times. A technology expert indicated that the phone would not be heard ringing by a caller if it had been submerged in water while switched on.
Besides, divers searched the Grand Canal and found nothing. The Dodder was searched, as were the shores of Dublin Bay. All to no avail.
The suicide theory was examined but his family and friends were convinced that the sociable young man, always at ease in company, had not been depressed or suicidal.
Trevor had phoned a pal at 4am and left a message, saying he would see him the next day. By his own account, he had had good fun at the party.
Was he harmed by the man seen on CCTV talking to him outside his office and then seen following him along the road? This was a strong theory which is still under investigation.
Did he emigrate to Alaska?
Two gardaí travelled to Anchorage in Alaska, which Trevor had visited shortly before he disappeared to see a young woman he had known.
Gardaí interviewed her and Trevor's two sisters travelled there with the same purpose.
That theory was ruled out.
Could Trevor have been murdered by muggers who made his body disappear by hiding it in a skip or big bin or by some other method? The visit of Bill Clinton to Dublin that weekend meant all big bins were collected and emptied for security purposes.
Could he have been the victim of a Tiger kidnap to get access to the bank?
The new garda operation stems from the claim that he was murdered and buried after an encounter on his way home.
Is is believed this latest search of woodland could finally solve a 17-year mystery.