A cheating husband faces trial for murder in city set against him

Shortly before Christmas 2002, a good-looking California fertiliser salesman called Scott Peterson began an affair with a massage therapist. He told her that he was a recently bereaved widower facing the prospect of his first Christmas alone.

Shortly before Christmas 2002, a good-looking California fertiliser salesman called Scott Peterson began an affair with a massage therapist. He told her that he was a recently bereaved widower facing the prospect of his first Christmas alone.

In fact his wife Laci was seven months' pregnant with their first child and very much alive, at least until Christmas Eve, when she vanished without a trace.

Three months later her decomposed body was dredged out of San Francisco Bay, where Mr Peterson, 31, said he had gone fishing the day she disappeared. The unborn child, which had become separated from its mother, was also found.

The police had no difficulty tracking Mr Peterson down because they were already deeply suspicious and had put tracers on his car. When they made their arrest he was playing golf in San Diego, not far from the Mexican border. He had dyed his hair orange, grown a goatee and was carrying $15,000 (£8,200) in cash.

To say that things do not look good for Mr Peterson as his trial gets under way today would be an understatement. Yet it has been much anticipated. The case has been little short of an obsession for the US cable news networks from the day that Mrs Peterson vanished 17 months ago, and its twists and turns have become the stuff of national soap opera, played out in People magazine and the supermarket tabloids.

In Modesto, the dusty farming city in California's Central Valley where the protagonists in this drama lived, the name Scott Peterson has become a synonym for despicable evil. He is seen as a liar, a cheat and a brutal murderer. The fact that Laci Peterson, 27, had a sweet, beatific smile only reinforced the notion that this was a shocking tale of innocence defiled.

The intriguing thing, however, is that the police seem to have little more than circumstantial evidence against Mr Peterson. The bodies of mother and child were too badly decomposed to determine a cause of death. Nobody saw Mr Peterson killing his wife at home on Christmas Day or the day before, as the police allege. Nobody, so far as we know, saw him wrapping the body in blue tarpaulin, or loading it on to his truck, or moving it to his new boat, or dumping it in San Francisco Bay - all elements in the prosecution's case. The police removed 50 bags of evidence from Mr Peterson's property at the time of his arrest, but the only forensic evidence made public so far is a hair found in a pair of pliers on Mr Peterson's boat that DNA analysis suggests probably belonged to Mrs Peterson. The prosecution has yet to demonstrate why this is evidence of foul play, however.

Nobody has yet explained how the baby became separated from its mother's body. Mr Peterson's lawyers believe the separation suggests she may have died much later than 24 December, possibly at the hands of abductors unconnected with Mr Peterson. No hard evidence of this alternate theory has emerged, either.

Then there is the troubling question of motive. Police and prosecution have speculated that Mr Peterson got rid of his wife to be with the massage therapist, Amber Frey, but that seems an extraordinarily drastic measure given that he had met Ms Frey only weeks earlier. She learnt the truth about her "widower" boyfriend by following the Mrs Peterson disappearance story on television, immediately went public to denounce him and has since become the star witness for the prosecution.

Mr Peterson is represented by Mark Geragos, a lawyer well-acquainted with media-circus trials. (His previous clients include Winona Ryder and Michael Jackson.)

He argues that the murder charges against Mr Peterson arise from the anger at his lies and adultery, not from the available evidence, and has also accused the police of focusing exclusively on Mr Peterson as a possible suspect, thus compromising their chances of identifying and catching the "real" killer or killers.

Last week a potentially valuable new witness emerged - a peace officer who claims to have seen two men throw Mrs Peterson into a van. Mr Geragos says the prosecution knew about this witness more than a year ago but only disclosed the evidence on the eve of the trial to give him less time to follow it up.

Even Mr Geragos acknowledges, however, that the weight of public opinion is against his client. He successfully lobbied to have the case moved from Modesto to Redwood City, just outside San Francisco, but opinion polls show the community there is no better disposed to Mr Peterson than in his home town.

Largely because of the saturation media coverage and the preconceived notions it has generated, it took 11 weeks to empanel a jury.