A second man has been arrested in connection with the deaths of two unarmed policewomen in a grenade and gun attack.
Greater Manchester Chief Constable Sir Peter Fahy said a 28-year-old man was detained in Hattersley on suspicion of conspiracy to commit murder.
Dale Cregan, 29, is still being questioned on suspicion of the deaths of the two police officers, and in connection with the murders of David and Mark Short who died earlier this year.
PCs Nicola Hughes and Fiona Bone had been called to an empty council house in Abbey Gardens in Hattersley after an apparently routine burglary report when they were attacked.
Witnesses said a number of bullets were fired, and a grenade was used.
Home Secretary Theresa May described the kilings as "savage acts of pure brutality"
"These were brave and talented officers who were going about their everyday duties, doing what they do, day in, day out, protecting the public, fighting crime and they were incredibly brave and their deaths are a reminder of what police officers face every day."
The minister was given a two-hour briefing by senior officers conducting the investigation into the deaths on a visit to the force's headquarters during which she reiterated government policy was against the routine arming of officers.
"I think that routine unarmed policing that goes on in our streets is right. I don't think this is the time to be calling for the arming of police."
Announcing the new arrest, Sir Peter said he could not be sure that all the grenades had been recovered from the area, and said a "threat" remained to officers.
"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. I would want that to be the message," he told a press conference.
"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."
It also emerged that one of the officers' tasers was found on the ground out of its holster at the scene.
PC Bone died at the scene and PC Hughes later in hospital.
Sir Peter said while the force "continued to mourn" the loss of two colleagues, the officers' families had "a huge amount to come to terms with".
Earlier it emerged that Cregan was held at gun point after walking into a police station.
Counter staff hit a panic button then asked him to go back outside Hyde police station in Greater Manchester, where he was confronted by armed officers who had been scrambled to the scene.
He had arrived at the station in a blue BMW around an hour after the officers had been attacked.
Sky's crime correspondent Martin Brunt said: "We can only imagine the reaction of the counter staff at the police station.
"This is an hour or so since the killing of the two police officers.
"They were clearly in some quandary about how to deal with him, and establish exactly who he was.
"He was kept talking, and whoever was dealing with him asked him to go back outside the police station.
"The panic button was pressed and by the time whoever was dealing with him had got him outside the police station an armed response unit had turned up.
"At that point Mr Cregan was held at gunpoint while police did what they could to establish what he was telling them, and exactly who he was."
Meanwhile, detectives are trying to piece together the final moments of the fallen officers, while forensic teams scour the area where they were killed for clues.
A police cordon remains in the area for specialist officers to carry out their examination of the site.
Earlier, a forensic expert could be seen up a ladder examining the gutter of a house on the street, while others checked drains.