Police are continuing to question a man after two unarmed policewomen were shot and killed when they answered a "routine call-out" about a burglary.
Dale Cregan, 29, was arrested after going to a police station in Hyde following the shooting. He is being detained on suspicion of killing the two officers.
He was already wanted in relation to the deaths of a father and son.
Fiona Bone, 32, and 23-year-old Nicola Hughes died in the gun and grenade attack in Hattersley.
Greater Manchester Chief Constable Sir Peter Fahy said: "Clearly we are devastated today by the loss of two of our officers.
"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."
He paid tribute to Miss Hughes, describing her as a "chatterbox" and a "great bobby" who was "always smiling".
He said Miss Bone was a "calm, gentle woman", an "excellent bobby" and had been in the middle of planning her wedding.
Prime Minister David Cameron said the killings were an "absolutely despicable act of pure evil".
"The cold-blooded murder of two female police officers doing their job out there protecting the public, another reminder of the incredible risks and great work our police service does.
"My thoughts and I think the thoughts of the whole country will be with their families at this impossibly difficult time."
Witnesses said a hail of bullets was fired and then a grenade was used during the attack, shortly before 11am on Tuesday.
One of the officers died at the scene. The second was critically injured and died later.
Cregan is being questioned on suspicion of the deaths of the two police officers and in connection with the murders of David and Mark Short.
David Short was killed at his home in Folkestone Road East, Clayton, Manchester, on August 10, while Mark was shot dead at the Cotton Tree pub in nearby Droylsden, on May 25.
Cregan was arrested in June in connection with the murder of Mark Short but was released on bail.
Four men have already been charged in connection with Mark Short's murder and will enter pleas at Manchester Crown Court in November.