Revealed: the final moments of gun-toting barrister

A police marksman who shot a drunken barrister who was firing a shotgun from a window insisted yesterday that what he did was "absolutely necessary" to save lives.

Mark Saunders, 32, was killed by armed officers who surrounded his £2.2m home in Chelsea, west London at the end of a five-hour siege. The officer, identified only as "AZ 12" to preserve his anonymity, told an inquest into Mr Saunders's death that he thought the barrister was going to kill colleagues on a nearby roof.

Mr Saunders had opened his kitchen window after firing from it during the siege on 6 May, 2008. AZ12 told Westminster Coroner's Court he was stationed at a house in Bywater Street, near Mr Saunders's home in Markham Square. "It's a physical thing – a show of force," he said. "The gentleman knows he's surrounded. He can see me, I can see him."

He added: "I'm trained to be there as a show of force, the barrier between the public and the bad man. That's what I do, and that's what I did." He said that after Mr Saunders opened the window he was "lowering the weapon towards my colleagues" on the roof of a neighbouring property. Asked if he shot Mr Saunders in self-defence, he said: "No, in defence of others."

Asked what he thought was going to happen, he said: "I thought he was going to kill them."

When asked if it was necessary to fire to defend them, or whether other action could have been taken, he said: "It was absolutely necessary. I cannot rely on their threat assessment of what I see in my position. I felt there was an imminent threat to their [lives]. If I had left it too late, they could have been dead. It was my duty as a police officer to defend my colleagues."

Mr Saunders triggered the siege when he fired his legally-held shotgun while on the phone to a friend at 4.40pm after an afternoon drinking binge. A second officer, identified only as "AZ15", told the hearing he went armed with his Glock 17 pistol to a house in Bywater Street and upstairs to a bedroom.

"Upon entering the room, I noticed straight away that the window had damage, and it appeared to be either birdshot or pellets from a shotgun," he said. "I made it clear to the occupants of the address to stay in the hallway and positioned myself to the left-hand side of the window."

AZ15 said he saw Mr Saunders standing at a window and firing a shot towards him, just as one of the occupants of the house he was in came into the room, so he fired back. "I feared for the safety of the person in the room, so until I could assess where that person was, I discharged two shots," he said.

Anticipating a second shot from Mr Saunders, he fired a third shot which struck the barrister's home, then he and a colleague helped to evacuate the occupants of the house in Bywater Street.

The inquest has previously heard that Mr Saunders died at 9.32pm after being shot at by seven police marksmen. Yesterday, a third officer, known as AZ6, told the inquest he had been watching Mr Saunders when the barrister disappeared from view, then re-emerged and shot at him. AZ6 said: "I don't want to sound Hollywood-ish, but I've never been shot at before. A large sheet of flame came out of the shotgun in my direction and I remember trying to pull [my] trigger at the same time. I know the shotgun can fire more than one round, so I fired again."

Earlier, Detective Inspector Steve Wagstaff, who was in charge of negotiations with the barrister during the siege, defended his decision not to allow Mr Saunders's wife Elizabeth to speak to her husband. Mr Saunders had indicated that he wanted to do so, and his family has criticised the Metropolian Police for not granting his request. Mr Wagstaff explained: "We had somebody in a flat, armed with a gun, shots had been discharged – our duty is to protect the public."

He said that given the same circumstances again, he would take the same decision.

Yesterday, the coroner released a video recording of Mr Saunders's final moments. The film, shown to the inquest jury on Wednesday, shows him drunkenly leaning out of his window and waving his shotgun towards of police officers.

The hearing continues.