'Steroids were the beginning of the end for my son. He was a quiet boy'

David Bieber seemed to be an ordinary American in Britain until the day he parked a stolen black BMW across a "Keep Clear" zone in Leeds and sat inside, flicking through the Racing Post and munching on a Galaxy hazelnut chocolate bar.

David Bieber seemed to be an ordinary American in Britain until the day he parked a stolen black BMW across a "Keep Clear" zone in Leeds and sat inside, flicking through the Racing Post and munching on a Galaxy hazelnut chocolate bar.

He had already shown that the British police did not consider him a threat by initiating his only encounter with them, reporting a man for harassment after a pub fight in Leeds in 2000. He was well-spoken, displaying the signs of his middle-class upbringing in the palm-fringed boulevards of Fort Myers, Lee County, Florida.

But when PC Ian Broadhurst tried to arrest him over the BMW last Boxing Day afternoon, Bieber reached for the 9mm semi-automatic pistol he was carrying and shot him.

Eight bullets were fired in five seconds from the Croatian-made gun, designed for police and military use. The last was dispatched as PC Broadhurst lay 25 inches in front of him, holding his hands over his face and pleading: "No, no, please don't shoot".

Acutely aware that a violent past which he had left behind in America was about to catch up with him, he then armed himself with 2,000 rounds and went on the run for four days.

As a teenager, life had seemed destined for a different course. A superb sportsman, he set a state record in the 100-yard breaststroke at the age of 13 and universities scouted him for their American football teams.

But he dropped out in 1984, endured the Marines for a year and drifted into the bodybuilding scene. He became a powerful individual at the town's Gold's Gym where, as he strove for perfection, he took and trafficked the nubain steroid.

He became violent. Three women filed papers in Lee County civil court claiming that Bieber had submitted them to violence and extortion. Then, in February 1995, he was suspected of paying $1,000 (£520) for the doorstep assassination of Markus Mueller, 29.

The German part-time actor was a rival in the lucrative steroid business and for the affections of Danielle Labelle - whom Bieber had married a week before the hit. Bieber did not co-operate with the inquiry but police convicted a middleman who arranged it, John Saladino, and the killer he hired, David Snipes. Both are serving long sentences.

Bieber's father, Frank, insists steroids changed everything. They were "the beginning of the end," he said. "He was once a quiet young man. Who thought it would turn out like this?"

Dr Harrison Pope, a Harvard professor of psychiatry, believes Mr Bieber may be right. "There have been many cases which I have been involved with which involve individuals with no prior history of violence, psychiatric disease or criminality who start taking anabolic steroids and then become a Jekyll and Hyde character," he said.

By the time the FBI began catching up with Bieber, he had assumed a new identity and fled for Europe. For $36 he had bought the birth certificate of Nathan Wayne Coleman, who was born two years before him but died in January 1975 in Atlanta, Georgia, aged six.

He arrived in Britain by ferry at Ramsgate in September 1995 on a tourist's visa under the Coleman alias. He met Denise Horsley - a divorcee with two sons. Just 17 days before his visa was due to expire, he bigamously married her at Kendal registry office, Cumbria. Ms Horsley had her suspicions about her new, fitness fanatic husband. She told police she knew him only as "Dave", that he took to staying indoors with the curtains shut, constantly dyed his hair different colours and that he insisted on no photographs at their wedding.

The couple were only married for a year, two years short of the period necessary to secure full British citizenship, but long enough to secure Bieber a registration card to work as a club doorman in Yorkshire - and tap into a new nubain trafficking market.

A low profile enabled him to evade detectives for several days after the shooting. Then the Leeds harassment complaint, made three years earlier, came back to haunt him. One of 3,000 callers who responded to a police description of the killer provided two mobile numbers for Coleman, one of which checked out on a West Yorkshire database against a number given by the individual who had made the harassment complaint, two years earlier. The officer who investigated the initial complaint identified him from CCTV pictures.

Last January, Bieber denied his crime; but in May, amid overwhelming evidence, he admitted it on grounds of diminished responsibility (owing to steroid abuse). Then, on 24 October, he created a "Mr X" - an anonymous American friend whom he claimed had carried out the crime. The story was preposterous but Bieber kept a confidence bordering on arrogance when he was cross-examined about it.

The similarities between Bieber and his "Mr X" (a Florida-based body builder who was "a bit dodgy and involved in criminal activity") suggest he may have been an alter ego. If this is so, the testimony provided a chilling clue about why he was armed with a 9mm pistol as he sat in the BMW 12 months ago. "Someone had pissed my friend off and disrespected him. He wanted to sort them out," Bieber said.