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 murder.
Dale Cregan, 29, who was one of the country's most wanted men, is also being questioned over the officers' deaths and the killings of father and son David and Mark Short.
Pcs Nicola Hughes and Fiona Bone were sent to investigate to what appeared to be a routine burglary call when they were fatally attacked.
Sir Peter said 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."