Pc Ian Terry was married with two children
A police officer who killed a colleague with a pump-action shotgun during a training exercise said the shooting had been an "involuntary act".
Pc Ian Terry, 32, was killed as Greater Manchester Police's firearms unit practised in a disused factory in 2008.
His colleague, a specialist firearms officer, known only as "Chris", said he had no intention of hurting Pc Terry.
He told an inquest in Manchester he had been "shocked" when the Remington 870 pump-action shotgun went off.
Pc Terry, who was not wearing body armour, was hit in the chest by specialist ammunition called round irritant personnel (RIP).
The father-of-two, from Burnley, was holding a handgun and playing a suspect during a "cops and robbers" vehicle training exercise involving about 20 officers.
Chris, who cannot be identified for legal reasons, gave evidence at Manchester Coroner's Court behind screens.
"When the weapon went off it was just complete shock," he said.
The inquest was told the officer had said in a statement to the Independent Police Complaints Commission (IPCC): "Looking back at this I did not mean to pull the trigger and it was an involuntary act."
Jonathan Hough, counsel for the Coroner Nigel Meadows, asked the officer: "You have described the act as an involuntary act, can we assume this was a shot you did not mean to fire and you are now very remorseful about?"
Chris replied: "I never had any intention of hurting anyone. I was there to cover the threat. I don't know why the trigger went off it just did.
"It was just horrible. I did not want to hurt anyone, especially not Ian.
"I think that was why I was so surprised when it did go off, I just did not expect it to happen."
'That's the threat'
Chris was a front seat passenger in one of three unmarked police cars - Alpha, Bravo and Charlie - which were tracking the the suspect vehicle, a Suzuki Vitara, in which Pc Terry was a passenger.
Chris's job was to shoot out the tyres of the suspect vehicle.
The Alpha car had hemmed in the suspect car and as the Bravo car pulled up for Chris to get out he said his "focus" was on a weapon being waved about by Pc Terry, playing the villain in the "target" car.
"My immediate reaction was, 'that's the threat,' that's what I need to be going for."
Lewis Brown, counsel for the other police officers at the incident, asked Chris about evidence given by them at the hearing.
Chris's colleagues had said RIP rounds would be used on the exercise, that officers should keep their shotguns down at all times, a "shoot-scenario" was to take place, only paint rounds were to be used in the shoot-scenario and that the safety catch was not to be taken off the shotgun until the muzzle was placed against the tyre to be shot out.
To all those questions, Chris said he could either not remember or was not given those instructions in a briefing before the exercise.
James Ageros, counsel for Chris, asked how the death of Pc Terry had affected him.
"I have been gutted ever since," he replied. "He was a colleague but I like to think he was one of the people I got along with better than anybody else.
"It just stays with me all the time. I know it is nowhere near as bad for me as the family, I just try not to think about it."
The inquest continues.