There had been no let-up in the investigation into the murder of Detective Garda Donohoe despite cutbacks in the force elsewhere.
At the time of the murder Justice Minister Alan Shatter was criticised for closing 900 garda stations around the country but 150 officers have been working on the murder case and there has been no cutback on these resources.
“This has always been a very difficult murder investigation, which will take time to solve, but everyone is confident the culprits will be brought to justice,” a garda source said.
Two of the five suspects are brothers and all them have close links to the GAA and republicanism in south Armagh.
Only one member of the gang is likely to be charged with murder.
The others are likely to face charges of possession of firearms and attempted robbery.
Vital information about their movements before and after the murder and robbery have been pieced together in the past few months.
The gang are known to gardai and would have been known by Detective Garda Donohoe.
Adrian Donohoe and his partner, Detective Garda Joe Ryan, were on escort duty at Lordship credit union when Adrian was killed with a shotgun.
He was shot at close range by a member of the gang when he got out of his unmarked patrol car in the credit union car park.
The CCTV footage of the murder shows that the gunman, who has been identified, intended killing Detective Donohoe.
Detectives on the case have been making painstaking but quiet progress.
They have gone through CCTV footage seized from 200 locations.
Gardai established the identity of the five early in the investigation. They were informally interviewed by the PSNI.
The gang are all in their 20s and were responsible for a crime spree along the Border in the past few years.