PSNI detectives investigating the death of Monaghan teenager Jason McGovern have launched a formal murder inquiry.
They said the 19-year-old died from head injuries sustained when he was attacked twice by another man in Omagh, Co Tyrone, early on Monday morning.
Detectives said Mr McGovern was punched in the head outside a pub and then assaulted again as he was waiting for a taxi back to Emyvale, Co Monaghan.
He was found dead at a friend's house in Emyvale on New Year's Eve.
Police are looking for a number of men who were involved in the assault, including a stocky man with red or fair hair.
The investigation is being led by the PSNI and supported by gardaí.
PSNI Detective Chief Inspector Richard Harkness said: "This is an assault that had no apparent motive other than young men out on a night out and fuelled by alcohol."
He appealed for taxi drivers and motorists at the Weigh Inn car park in Omagh to come forward.
The detective said he is especially keen to speak to two middle-aged men who helped Mr McGovern into the taxi with his friend after the assault. The men are not linked to the assault.
Mr McGovern, who cared for his mother who suffers from multiple sclerosis, was a Eucharistic minister in Emyvale and local priest Fr Macartan McQuaid said the community was shocked by his death.
He said: "There is a great sense of loss in the community. He had many friends. A wide circle of friends.
"He was an enjoyable young fellow and he was a great young lad to banter and chat."