A 61-year-old man has been arrested in England by detectives investigating the sectarian murder of Paul McAuley in Derry.
The man was detained in Kent and taken to Belfast for questioning.
Mr McCauley, a Catholic, spent almost a decade in a vegetative state after being beaten by loyalists in Derry's Waterside area in 2006. He died last June aged 38.
The suspect was arrested on Wednesday, with police announcing the development on Thursday morning.
Two other men, aged 27 and 28, were detained in Derry on Wednesday.
The pair had been arrested last year and were released on police bail but were re-interviewed at Strand Road police station on Wednesday after a court approved their further detention.
The two men remained in custody on Thursday.
A total of 17 people have been detained over Mr McCauley's death.
The father-of-one was 29 when he attended a barbecue for a friend who was moving away.
A gang of up to 15 people emerged from nearby bushes and attacked him and two friends as they were clearing up after the meal in the early hours of the morning.
He suffered severe head injuries and died last year.
Mr McCauley's family has pursued a long campaign for justice.
Piper John McClements (24) previously known as Daryl Proctor, from the Fountain area of Derry, has been charged with the civil servant's murder.
The PSNI officer leading the investigation, Detective Chief Inspector Michael Harvey, said: "We said after Paul died that this investigation would take on a renewed momentum and this momentum is continuing.
"One person has been charged with murder and another individual has been reported to the Public Prosecution Service. Detectives are available to speak with anyone who decides they want to talk to us.
"Even after almost 10 years, it is not too late to do the right thing and come forward. Anyone with information about the attack and its tragic outcome can speak to detectives on the non-emergency number 101."
