One of Britain's most wanted men was accused of luring two unarmed female constables to their deaths yesterday.
Greater Manchester chief constable Sir Peter Fahy said the officers had been sent to investigate what appeared to be a routine burglary report when Dale Cregan (29) attacked them with a gun and a grenade.
"It would appear Cregan has deliberately done this in an act of cold-blooded murder," he said.
He said Cregan's motive for the attack was "impossible to fathom".
After the murders, Cregan gave himself up at nearby Hyde police station in Greater Manchester.
He was already wanted in connection with separate gun and grenade attacks.
Sir Peter named the officers as Fiona Bone (32) and Nicola Hughes (23).
Eyewitnesses said a hail of bullets had been fired and then a grenade used during the attack shortly before 11am.
Miss Bone died at the scene. Miss Hughes was critically injured and died a short time later.
"I just heard gunshots, bang, bang, bang - around 10 of them, then a pause and a big explosion," window cleaner Warren Shepherd said.
The scene was cordoned off with a heavy police presence. A fleet of vans and ambulances was parked at the top of the road as a helicopter hovered overhead.
A controlled explosion is believed to have been carried out on a dark blue BMW coupe parked outside Hyde police station according to nearby residents, who reported hearing a loud bang and spotted a plume of smoke.
The vehicle is suspected to have been used by Cregan to drive from Hattersley to hand himself in to police.
Sir Peter paid tribute to Miss Hughes, describing her as a "chatterbox" and a "great bobby" who was "always smiling".
He described Miss Bone as a "calm, gentle woman" and an "excellent bobby" who had been in the middle of planning her wedding.
"This is one of the darkest days in the history of the Greater Manchester Police, if not for the police service overall, because we have lost two deeply loved and valued colleagues, because they are part of our team. Policing is very much a family," Sir Peter told a press conference at Greater Manchester Police headquarters.
"But also because of the huge efforts that officers had been making to arrest and detain Dale Cregan.
"Obviously the officers involved in that inquiry are shattered by this outcome."
The chief constable said it was routine to send unarmed officers to a burglary call.
"We believe that Dale Cregan was in a house in Abbey Gardens overnight and at some point this morning has either himself made a call or had somebody else make a call reporting a burglary," Sir Peter said.
"This particular address was not known to us. So as would be routine, two unarmed officers were sent to the scene.
"When they arrived, it appears that Cregan emerged into the road and killed these two officers.
"A firearm was used. A grenade was also used."
Asked if the grenade had been thrown directly at the two officers, Sir Peter said: "Certainly we believe the grenade was thrown at the officers but we have not been able to be specific about the injuries the officers suffered or how they died."
Sir Peter said he believed Cregan had been "protected by a criminal conspiracy to harbour him".
Two people from the house in Hattersley, a man and a woman, were helping police with inquiries yesterday.
Last night Cregan was being questioned on suspicion of the murder of the two officers and two other murders.
Cregan, who has no left eye, had been the subject of a huge manhunt after the murders of David Short (46) and his son Mark (23).
David Short was killed at his home in Clayton, Manchester, on August 10.
Mark was gunned down at the Cotton Tree pub in nearby Droylsden on May 25.
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