Police have arrested a second man in connection with deaths of two unarmed police women in Greater Manchester.
Sir Peter Fahy, Greater Manchester Chief Constable, said a man was detained in Hattersley on suspicion of conspiracy to murder.
Yesterday, 29-year-old Dale Cregan, who was one of the country's most wanted men, was also being questioned by police after walking into a police station in Hyde.
The news came as Sir Peter defended the decision to bail Dale Cregan.
Sir Peter Fahy said in a statement that the force had no choice but to release Mr Cregan and described the decision as “absolutely normal”.
Constables Nicola Hughes, 23, and Fiona Bone, 32, were killed when they attended a routine burglary report at a residence in Abbey Gardens, Mottram yesterday.
It is believed they were attacked with a gun and a grenade.
Sir Peter said today he could not be sure that all the grenades had been recovered from the area, and that officers remain in danger.
"We are not confident that we have recovered all the grenades, we don't know for certain, so we've made it clear to our officers that the threat is still there," he told reporters.
"I would want that to be the message, this has been a long-standing criminal feud between different outfits in Manchester and in the Tameside area, and that threat is very much there.
"As we've indicated as part of this inquiry we've had to issue essentially what we call Osman warnings, threat notices, to a large number of individuals who we felt could be at risk as a result of this particular series of events."
Greater Manchester police said yesterday that it appeared as though the two officers had been deliberately lured to the scene.
Eyewitnesses described a hail of bullets being fired and then a grenade being used in the attack, shortly before 11am.
Pc Bone died at the scene, Pc Hughes was critically injured during the attack and died later in hospital.
The force said that one of the officers' Tasers was found on the ground out of its holster at the scene.
Sir Peter yesterday paid tribute to the officers, describing Miss Hughes as a “chatterbox” and a “great bobby” who was “always smiling”.
He said Miss Bone was a “calm, gentle woman” and an “excellent bobby”.
Police said Miss Bone had been in the middle of planning a civil ceremony for her same-sex partnership.
Shortly after the incident, Dale Cregan, 29, who was being hunted by police for questioning over two separate murders, handed himself in at a police station in Hyde.
Detectives are continuing to question Mr Cregan over the deaths of PCs Hughes and Bone.
Today it emerged that Mr Cregan was released on bail following questioning over the shooting of Mark Short in a Manchester pub.
Police have suggested that he had been hidden in the community as part of a 'criminal conspiracy'.
Commenting on the bail decision, Chief Constable Sir Peter Fahy said in a statement: “It is absolutely normal in the course of complex crime inquiries that when people are arrested there are occasions where there is insufficient evidence available for them to be charged.
“In those circumstances suspects have to be released on bail as there are strict time limits covering how long suspects can be held in custody without charge. That is exactly what happened in this case.”
Cregan, who only has one eye after reportedly losing the other during a fight in Thailand, was wanted for questioning in relation to the shooting of Mark Short, 23, in a Manchester pub, and Mr Short's father, 46, who was murdered in a gun and grenade attack in August.
Four men have already been charged in connection with Mark Short's murder and will enter pleas at Manchester Crown Court in November.
Following Cregan's release on bail he went on the run, becoming one of Britain's most wanted men prompting a police manhunt.
A £50,000 reward had been offered for information leading to his arrest, and his image had been shown on the screens at a Manchester City football game.
At a press conference yesterday, Sir Peter said it was one of the “darkest days” in the history of the police service.
He told reporters: “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 also said the decision to send two unarmed officers to a burglary report was routine, saying he believed someone had deliberately made the false report in order to lure the officers to the house.
At yesterday's press conference Sir Peter said he was not aware that Cregan had contacted police at any time during their manhunt or made any threats to police officers.
The shootings have once again reignited the debate over whether police officers should be armed. Speaking yesterday Sir Peter said he believed 'passionately' that police should remain unarmed.
The chairman of the Greater Manchester Police Federation Ian Hanson called yesterday's killings “the slaughter of the innocents”.
He said: “I'm going to look beyond the uniform here. What we've got are two young girls that went out this morning and they've got an absolute right to come home tonight to their loved ones. This is cold-blooded murder. It's the slaughter of the innocents. GMP is a family.”
Prime Minister David Cameron said the killings were an “absolutely despicable act of pure evil”.
In a statement today, Pc Hughes's family said: “Nicola was our only daughter and a beautiful child. She was always happy with life and lived for her family.
“She had an infectious personality and sense of humour and was a very caring and loving girl. When she left the house this morning she was going to the job she loved.
“Nicola always wanted to make a difference and, in doing so, she made such a big difference to everyone she knew. She cared about everyone and especially her colleagues.
“Nicola was only 23 years old and had the whole of her life in front of her.
“We cannot express how we feel today except to say we have always been exceedingly proud of Nicola and always will be. She knew she was loved by us all and we shall all miss her dreadfully.”
Home Secretary Theresa May is on her way to Manchester to meet Sir Peter later today, the Home Office said.
It is understood she has cut short her holiday in the wake of yesterday's murders.
Greater Manchester police today opened a book of condolences for the two officers on the police website, they said 2,600 messages had already been posted.
Manchester United announced that players would wear black armbands during their Champions League match with Galatasaray as a mark of respect.