Detectives investigating the death of off-duty police constable Neil Doyle have arrested a man on suspicion of murder, Merseyside Police said.
The 28-year-old suspect handed himself in to police last night and is currently being interviewed by detectives, officers said.
PC Doyle, 36, was attacked in Liverpool city centre in the early hours yesterday during a Christmas night out with colleagues.
He was due to go on his honeymoon next month.
PC Doyle was with two other off-duty officers when they were attacked by three men in Colquitt Street at around 3.15am.
His colleagues were both treated in hospital for facial injuries.
A Merseyside Police spokesman said detectives were investigating the possibility that the officers were recognised from their work.
"It's one line of inquiry that we are looking at but it's by no means the set-in-stone motive," he said.
PC Doyle, who joined the force in May 2004, was taken to the Royal Liverpool Hospital after the attack, but died a short time later.
The officer, who got married in July, had received a commendation for his actions in arresting three men after a violent robbery.
He was based at Eaton Road police station in West Derby.
Peter Singleton, chairman of Merseyside Police Federation, said the police community was "devastated" by Pc Doyle's death.
"Devastated is the nearest word I can think of," he said. "His family, friends and colleagues are absolutely devastated. I spoke to the colleagues who were out with him and they were in absolute bits.
"He exemplified the British bobby. He was a solid, good, hard-working, honest copper. Losing a colleague like Neil in such a tragic way is absolutely devastating."