A police firearms officer told an inquest today how he exchanged fire with a barrister who was shooting from a window at his home.
Mark Saunders, 32, was shot dead by police marksmen surrounding his £2.2 million property in Markham Square, Chelsea, on May 6, 2008, at the end of a five-hour siege.
The officer, known only as AZ 15, to preserve his anonymity, told Westminster Coroner's Court of the exchange of gunfire early in the stand-off.
He and colleagues had gone to the scene after receiving reports that an incident was developing.
The officer, who was armed with a Glock 17 self-loading pistol, went to a house in neighbouring Bywater Street and climbed up 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."
At first he thought that the gunman was in the garden but then saw him standing at a window - well within the range of his Glock.
"I could see he was carrying a long-barrelled weapon. Initially it was facing towards the ground.
"At the point where I noticed he was carrying the weapon, it was levelled in the direction of the area I was in and a shot was discharged towards my direction."
AZ 15 said he became aware that one of the occupants of the house had come into the room so he fired two shots back at the gunman.
"I feared for the safety of the person in the room, so until I could assess where that person was, I discharged two shots from my weapon."
He also fired a third shot, because he anticipated a second shot from the gunman, he added.
Within seconds of another officer known as AZ 14 taking over his position with a Heckler & Koch MP5 carbine, which has a longer range, the gunman fired a second time.
"The shot struck the masonry of the window surround of the room we were in."
He helped evacuate the man and woman from the house.
Earlier today an officer co-ordinating negotiators at the siege said it did not cross his mind that Mr Saunders' wife should be allowed to go to him.
The inquest has heard that his family criticised police for blocking his wife Elizabeth despite her husband's repeated requests to speak to her.
Detective Inspector Steve Wagstaff was asked today if it had crossed his mind at the beginning of the incident that Mrs Saunders or his close friend Michael Bradley should be allowed to attend.
The officer, who was co-ordinating hostage negotiators at the scene, said: "Not in the circumstances."
Asked why not, he said: "We had somebody in a flat, armed with a gun, shots had been discharged - our duty is to protect the public."
Asked about a suggestion that conversations between someone in his role and his senior officer should be recorded, he said he agreed with the Metropolitan Police Commissioner that this could restrict free thinking in tense and difficult situations.
But when asked for exact details of what he had passed on about Mr Saunders' drunken condition, he said he could not remember.
"I would have summarised Mark's demeanour at every practical opportunity," he said.
The family yesterday watched harrowing footage that showed the moment Mr Saunders died in a volley of bullets.
His sister Charlotte wept as a dramatic two-and-a-half hour film was shown to the inquest jury.
His widow walked out of the court as footage shot by a police helicopter and an audio recording of negotiations was played.
The inquest, sitting in Marylebone, has heard how the legal high-flyer waved a shotgun from his smashed kitchen window before fatefully pointing it towards armed officers.
He sparked the siege when he fired his legally held shotgun while on the phone to a friend at 4.40pm after a lonely afternoon drinking binge.
Highly trained negotiators started trying to open a dialogue by calling his mobile phone at about 7pm.
Mr Saunders played music loudly as he staggered around swigging wine, falling down the stairs and repeatedly vomiting violently.
The inquest has heard he texted a friend with a line from the song by The Doors, The End, used in the soundtrack to Apocalypse Now, saying: "This is the end my only friend, the end."
Tense discussions entered a final, terrifying phase when Mr Saunders blasted the weapon through the window at 9.09pm, provoking two police shots that hit no-one.
At 9.31pm, he brought the gun out of the window and waved it erratically in the air as a police officer shouted, "Put the gun down" through a loud hailer.
One minute later, Mr Saunders, illuminated by a spotlight from a police helicopter, slowly lowered the barrel before being hit in the head and chest by five police shots.
Another firearms officer, known only as AZ 6, said Mr Saunders fired towards him at 9.09pm and he fired back.
The officer was keeping vision and containment on the gunman as Mr Saunders drank what the officer believed to be red wine from an oversized wine glass.
Mr Saunders disappeared from view for a short time.
"Then I was aware that the shotgun he had was coming up towards where I was, level with myself."
He added: "I don't want to sound Hollywoodish, 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 the trigger at the same time.
"I know the shotgun can fire more than one round, so I fired again."