The Ayrton Senna manslaughter trial comes to a close today, exactly a year after Formula One team chief Frank Williams and five other defendants were formally indicted.

However, Judge Antonio Costanzo's long-awaited ruling is likely to raise as many doubts as answers about the death of one of Formula One motor racing's greatest drivers.

The main question that Senna's fans want answered is what really caused the driver's Williams to hurtle off the track and into a concrete wall at around 220 kph as it entered the Tamburello bend during the eighth lap of the San Marino Grand Prix.

The prosecution alleges that a poor weld on Senna's steering column snapped causing him to lose control of his car.

It has also claimed that the way the track was maintained could also have contributed to the accident.

The former assertion has been vigorously challenged by Williams as well as other drivers.

Lawyers for Williams have indicated that Senna, a driver who rarely made mistakes, could have lost control while trying to avoid a piece of debris on the track.

Three track officials were charged with Williams and Williams's technical director Patrick Head and former designer Adrian Newey.

However, last month prosecuting magistrate Maurizio Passarini made a dramatic about-turn when he asked for manslaughter charges against Williams and the three track officials to be shelved "for not having committed the offence".

However, Head and Newey still face possible sentences since Passarini asked for them to be given one-year suspended sentences.

A guilty verdict on any of those involved could potentially pose problems for the sport in Italy.

The world body FIA warned when the trial opened that drivers and teams might be unwilling to race in Italy in the light of the court action.

If the judge hands down a not guilty verdict, ruling that the steering column and track were not at fault, then the question will remain. What did cause Senna's death?