PC Fiona Bone (L) and PC Nicola Hughes were killed in the incident
A man suspected of killing two female police officers in Greater Manchester had been arrested three months ago over a fatal pub shooting, it has emerged.
PC Nicola Hughes, 23, and PC Fiona Bone, 32, were killed in a gun and grenade attack after being called to investigate a report of a burglary.
According to the BBC, Dale Cregan is being held on suspicion of their murders and two others.
In June, Cregan, 29, was questioned over the shooting of Mark Short in Manchester and released on bail.
Detectives are continuing to question Cregan over the deaths of PCs Hughes and Bone.
The police constables had been sent to investigate what appeared to be a routine burglary report in Abbey Gardens, Mottram, when they were attacked with a gun and a grenade.
Police said it appeared they had been deliberately "drawn" to the scene.
A witness at the scene in Tameside reported hearing 13 gunshots and an explosion shortly before 11:00 BST on Tuesday.
One of the officers died at the scene and the second was critically injured and died afterwards, police said.
Cregan was detained when he walked into Hyde police station a short time after the incident.
Two people from the house, a man and a woman, are helping police with inquiries.
Greater Manchester Police Chief Constable Sir Peter Fahy said it may have been one of the "darkest days" in the history of the police service.
Sir Peter said the officers exemplified the very best of British policing.
He said Miss Bone was a "calm, gentle woman", an "excellent bobby" and had been in the middle of planning her wedding.
He paid tribute to Miss Hughes, describing her as a "chatterbox" and a "great bobby" who was "always smiling".
The outrage prompted renewed calls for the routine arming of police.
But Sir Peter said his force believed "passionately" that police should remain unarmed, despite the tragedy.
Ian Hanson, chairman of the Greater Manchester Police Federation, said: "What we've got are two young girls who went out this morning and they've got an absolute right to come home to their loved ones.
"This is cold-blooded murder, the slaughter of the innocents."
Prime Minister David Cameron said the killings were an "absolutely despicable act of pure evil".
Association of Chief Police Officers president Sir Hugh Orde said the deaths were "deeply sad news for the police service".