Detectives have been granted more time to question a man suspected of murdering off-duty police constable Neil Doyle.
Pc Doyle, 36, was attacked in Liverpool city centre in the early hours of Friday morning during a Christmas night out with colleagues.
A 28-year-old man from Huyton was arrested on suspicion of murder later that day.
Merseyside Police have been granted permission to keep him in custody for further questioning until tomorrow night.
A 30-year-old man, also from Huyton, was arrested yesterday and remains in custody.
Both men were also arrested on suspicion of assaulting two other off-duty officers who were attacked alongside Pc Doyle by three men in Colquitt Street at around 3.15am on Friday.
The two officers were both treated in hospital for facial injuries.
Pc Doyle's widow Sarah said in a statement: "Neil was very well loved by all of his family, friends and colleagues and it is a great loss to us all.
"We are finding it extremely difficult to come to terms with what has happened and need time to be left to grieve."
The couple got married in July and were due to go on their honeymoon next month.
A post-mortem examination concluded that Pc Doyle died from a fatal bleed around the brain.
This was caused by damage to major blood vessels supplying the brain and is consistent with an assault.
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 was previously awarded 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."