Nine people are still being questioned in connection with three dissident republican murders in Northern Ireland.
Detectives have been given an extra five days to question a 21-year-old man in connection with the murder of Constable Stephen Carroll.
Five people are being held over the killing, including a man and a woman arrested in Craigavon on Saturday.
Also on Saturday night, a fourth man was arrested over the murders of two soldiers at an Army base last week.
Constable Carroll, 48, was shot while on duty in Craigavon, on Monday by the Continuity IRA.
Soldiers Mark Quinsey, 23, from Birmingham, and Patrick Azimkar, 21, from London, were shot dead at Massereene barracks in Antrim last Saturday by the Real IRA.
The man who was arrested on Saturday night over the killings was detained in the Antrim area.
Appeal
Detectives revisited the scene of the soldiers' murders on Saturday night.
Detective Superintendent Peter Farrar appealed for the driver of a horse lorry, which passed Massereene on the Randalstown Road shortly before the shooting, to contact police.
"We strongly believe that the blue/green Vauxhall Cavalier, TDZ 7309, that was used by the killers to attack the barracks, may have overtaken this lorry," he said.
The detective also called for anyone who was in an industrial estate opposite the base last Saturday night to get in touch.
Det Supt Farrar said the killers had made an unsuccessful attempt to burn-out the getaway car after the murders.
"As a result, we now have a number of forensic opportunities that we are exploring," he said.
Roman Catholic, Church of Ireland, Presbyterian and Methodist clergy held special services on Sunday where church leaders asked people to wear purple ribbons in protest at the recent murders.
There were also prayers for an end to violence.
'Very dangerous'
Police have said the number of republican dissidents trying to wreck the Northern Ireland peace process is about 300.
Chief Constable Sir Hugh Orde told the BBC that intelligence clearly showed the numbers intent on violence was a tiny proportion of the population.
Sir Hugh told BBC1's Andrew Marr Show: "Of course, the threat is very dangerous, that's been evidenced in the last week, but it's a very small group.
"Three hundred people in a population of 1.7m people puts it in perspective but it's a threat we take seriously.
"We have mobilised against it and as you've seen arrests have been made."
He rejected "ridiculous" media stories that attacks on politicians elsewhere in the UK were being hatched.

Meanwhile, police investigating the Massereene murders came under petrol bomb attack from rioters in Lurgan.
One officer was injured when he was hit on the arm with a brick. Two teenagers were arrested.
On Sunday, a security alert in the Allenhill Park area of Lurgan was declared a hoax. Two controlled explosions were carried out.
Police had been carrying out searches in Lurgan where prominent republican Colin Duffy was earlier arrested over the killingsThis article is from the BBC News website. © British Broadcasting Corporation