A police officer killed in a gun-and-grenade attack may have been trying to defend herself when she died, it has emerged.

An eye-witness has said they saw a Taser stun gun in the hand of Pc Fiona Bone, 32, as her body lay on the ground outside the house they were visiting in Mottram on Tuesday morning.

The unnamed witness said: “She had a Taser in her hand and she was laying by the window of the house.”

She died at the scene and her colleague Pc Nicola Hughes died later in hospital.

Residents reported hearing an explosion from a grenade and up to 13 shots being fired.

A spokeswoman for Greater Manchester Police confirmed a Taser stun gun was found out of its holster on the ground beside the two stricken officers, although they added it was unclear to which officer it belonged. Forensic experts are now examining it.

It came as chief constable Sir Peter Fahy warned that his officers could still be at risk from grenades in the wake of the double murder.

Sir Peter said he was not sure that all the grenades had been recovered from the area after the unarmed officers were fatally attacked.

Speaking at a press conference at GMP’s headquarters in Newton Heath, he confirmed that the crime scene at Abbey Gardens, Mottram, had been preserved to allow fragments of the device, which was used in the killings, to be recovered.

He also revealed that the firearm used in the incident had been recovered and said they were determined to bring to justice anyone who had been engaged in a ‘criminal conspiracy’.

Sir Peter said: “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, 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.”

Sir Peter told the conference that the women had been sent to investigate to what appeared to be a routine burglary call when they were murdered – and there was no intelligence or information to suggest that the address posed any greater threat than any other call.

He added: “I don’t think we have said there are any questions about our procedures.

“There was nothing in our intelligence systems or information systems that had come to light that indicated that the risk at this address was any greater than any other that we have been called to.

“We have had armed officers on patrol in those areas, 24 hours a day, seven days a week. We get hundreds of calls to incidents, all sorts of crimes like anti-social behaviour, and clearly we can’t send armed officers to every single one of those. It’s just the nature of policing that unarmed officers every day go to incidents not knowing what might be the risk or the threat or knowing what they are walking into.”

A second man has been arrested in connection with the deaths. Greater Manchester Chief Constable Sir Peter Fahy said a 28-year-old man was detained in Hattersley on suspicion of conspiracy to murder.

He also thanked the public for their support – and said his colleagues had been overwhelmed by the outpouring of grief from the community.

“I would like to thank the public for this tremendous show of support. It means a huge amount to us at this difficult time.

“The whole force and indeed the whole police service is devastated by the deaths of these two brave colleagues but to know that at this difficult time that the public supports what we do and supports so strongly what we do and is giving support to the families, that is really important to us.”

Sir Peter paid tribute to the dignity of the families of Pc Bone and Pc Hughes – and said relatives of the women were incredibly proud of them and knew they had died doing a job that they loved.