The trigger was pulled by a young New Zealand woman with degrees in mathematics and chemistry, a bright personality and a respectable family background. But why 28-year-old Maori Te Rangimaria Ngarimu - known as "Sparky" - acted as a hired assassin for Deith Bridges and Paul Tubbs remains a mystery.
She does not fit the image of a ruthless hit woman, coming from a respectable Christian family who live in a small village on South Island. At school she excelled at hockey and netball. She is fluent in Japanese and has represented New Zealand at surfing. Everyone interviewed by the police described her as "bright, bubbly, very personable and good company".
Yet, armed with a gun and a photograph of Graeme Woodhatch, 38, a roofing contractor, she went to the Royal Free Hospital in north London in May 1992 where she found her victim, whom she had never met, using a pay phone outside his ward. She shot him four times in the head and body.
She wept as she told the Old Bailey: "I had my hand on the gun and took off the safety catch. I was pacing up and down deciding whether to do it or not. Then something just snapped and I did it. There were four shots but I remember pulling the trigger only once. That shot him in the face. I remember seeing him rolling around on the floor screaming. He had his hands on his face."
She said she had agreed to the killing after being promised £7,000 - although she only received £1,500 - which she was going to use to buy what she described as a "house bus" or mobile home. She fled to New Zealand after the killing.
Ngarimu, who has already been convicted of murder, had been hired by Tubbs, 35, of Enfield, north London, and Bridges, 22, of Leeds. They, like the assassin, made unlikely big time criminals.
The contract killing was not a underworld hit involving a gangland war, but a row between business partners.
Tubbs, who had left school at 15, had gradually built up his roofing company and was terrified that his more experienced partner, Mr Woodhatch, was going to take control.
Before joining up with Tubbs, Mr Woodhatch had been a very successful roofer, particularly in the 1980s, when he owned a big country house and a Porsche. Tubbs suspected that his partner was stealing money from the firm and issued a series of civil actions at the High Court. An estimated £50,000 is believed to have gone astray from the company.
Deith Bridges, who was born in Norwich but had lived in New Zealand, was employed by Tubbs. He knew Ngarimu from a time when they had both worked at the Carnarvon Castle pub in Camden, north London, a popular meeting place for Kiwis living in the capital. Ngarimu described their relationship as "like brother and sister". Bridges, too, came from a "respectable" family. His father is a retired school teacher.
Ngarimu told the court that Bridges had asked her to "knock off" Mr Woodhatch. "I said `Yeah, I'll do it.' I did not believe it was actually going to happen."
For his pains Bridges got £3,000 and the gratitude of Tubbs. Neither man had been convicted before of any serious crimes. Neither man was joking about the hit.
The day before the killing, Ngarimu said, she was approached by Bridges, who gave her a gun wrapped in a towel and some bullets. "He said that I was to make sure I shot him four times. Twice in the head and twice in the chest. I didn't think it would actually go ahead. I knew hardly anything about Woodhatch."
Bridges himself later became a victim when he was shot while on bail in west London and needed hospital treatment. That attack is still being investigated by police.
Scotland Yard detectives became suspicious of Ngarimu when she left the country immediately after the shooting of Mr Woodhatch. After she was interviewed in New Zealand, local police asked her voluntarily to return to Britain.
A lawyer advised her against doing so, but during a visit to Auckland, she said, she went into a church. She told police that suddenly a weight was lifted from her shoulders and she knew she had to speak out about the killing. Bridges' counsel suggested in court that Ngarimu's conversion was a ruse to get the shortest sentence possible.
Whatever the reason, there is still no explanation for why she committed such a horrendous act on the promise of a relatively small amount of money.
One of the detectives involved in the case said: "The big question for us still, is why. Why, why, did she do it? Ninety-nine per cent of the population would be ruled out [because they could not] kill."
Ngarimu, whom her mother, a civil servant, described as "at peace with herself", now awaits sentencing for murder on Thursday.