PSNI officers were today expected to launch a murder investigation.
Witnesses are understood to have told police that Jason was set on after trying to act as a 'peacemaker' during an altercation between revellers.
Officers today made a fresh appeal for those involved to come forward.
Investigators believe he was first assaulted in a pub on John Street just after midnight on Sunday night after he tried to break up a fight.
Jason continued on his night out before he was attacked outside a nightclub at about 2am.
He managed to make his way to a friend's flat in Emyvale, Co Monaghan, but was found dead shortly after midday on New Year's Eve.
It is understood that he had complained of headaches before going to sleep.
CCTV footage of both incidents was being examined today.
Officers have identified a man of stocky build with either blond or red hair whom they believe was involved.
Meanwhile, the close-knit community of Tydavnet, Co Monaghan has been plunged into grief.
It emerged that Jason often cared for his mother, Kathleen, who is understood to suffer from multiple sclerosis and is wheelchair-bound.
"His mother is very, very ill and he was very caring towards her and also his grandmother," said local priest Fr Macartan McQuaid.
"He was such a lovely young fella, the family are just shattered. It is such a waste of a young life."
Jason, a second-year student at Sligo IT, where he studied theatre management, was with a group of 20 friends who travelled to Omagh for a night out on Sunday.