Change to rule allowed Dobson to be retried for Stephen Lawrence's murder

Gary Dobson could not have been convicted of murdering Stephen Lawrence nearly 19 years ago if the law had not been changed in 2003.

Dobson, Luke Knight and Neil Acourt were brought to trial in 1996 as the result of a misguided private prosecution initiated on behalf of the Lawrence family. The three defendants were acquitted on the judge's direction because of insufficient evidence.

As the law then stood, none of them could be tried again for the same offence. A prosecution would have been barred under the old common law principle known as autrefois acquit, more commonly referred to as the rule against double jeopardy.

Even so, Dobson, Knight and Acourt were identified by Sir William Macpherson of Cluny, the retired high court judge whose report into the Lawrence killing was published in 1999, as "prime suspects" for the murder. The other two prime suspects, according to Macpherson, were Jamie Acourt and David Norris - the second of whom has also been found guilty of murder today.

The Lawrence family had attempted to prosecute Norris and Jamie Acourt too. But there was insufficient evidence even to justify sending them for trial. Since Norris had never faced a jury, he could not rely on the double jeopardy principle when the decision was taken to charge him, alongside Dobson, with the Lawrence murder.

How, then, was it possible to bring Dobson to trial? In a far-sighted recommendation, the Macpherson inquiry recommended in 1999 that the double jeopardy principle deserved "debate and reconsideration", perhaps by the law commission. If the law was changed, Macpherson predicted, fresh trials after acquittal would be exceptional and appropriate safeguards would be essential. But pointing out that Dobson, Knight and Neil Acourt could not be tried again as the law then stood, however strong any new evidence might be, the Macpherson inquiry suggested that "perhaps in modern conditions such absolute protection may sometimes lead to injustice".

The government's law reform advisers did indeed recommend reform of the double jeopardy rule in 2001 and the law was changed in the Criminal Justice Act 2003. That legislation says the court of appeal must order a re-trial if there is new and compelling evidence and it is in the interests of justice for an order to be made.

The new law was brought into force in 2005 and used successfully the following year in a case where an acquitted murderer had subsequently confessed.

At that time it was not thought that the reform would lead to convictions in the Lawrence case. Quite apart from the perceived lack of evidence, it was thought that any of Macpherson's "prime suspects" might argue that they could not receive a fair trial in view of prior prejudicial publicity.

The law commission also drew attention to the conceptual problem inherent in any retrial ordered by the court of appeal in a high-profile case: an intelligent jury would know not only that a case was being heard for the second time ? which is not, in itself, prejudicial ? but also that senior judges had previously regarded the new evidence as compelling. To avoid the jury becoming aware of this, the court of appeal is permitted to impose reporting restrictions pending a retrial.

In Dobson's case, three appeal judges ordered a retrial in May 2011. The lord chief justice, Lord Judge, said:

If reliable, the new scientific evidence would place Dobson in very close proximity indeed to Stephen Lawrence at the moment of and in the immediate aftermath of the attack, proximity, moreover, for which no innocent explanation can be discerned.

The appeal judges concluded that there was "sufficient reliable and substantial new evidence to justify the quashing of the acquittal and to order a new trial". They permitted this finding to be reported at the time and their judgment remained accessible online throughout the trial. However, the appeal judges postponed publication of their detailed reasons until the case had ended.

Opposing the CPS application for a retrial at a hearing last April, Dobson's counsel argued that adverse publicity would make it impossible for the jury to try the case with the necessary fairness. Although that argument was dismissed, it may well form the basis for an appeal. One of the charges against Levi Bellfield was dismissed in June because of adverse publicity after he was convicted of murdering Milly Dowler.

Even so, courts tend to take a robust approach to potentially prejudicial publicity, and rightly so. If we are going to keep juries we need to trust them to judge cases on the evidence, however irresistible the temptation to consult readily available sources of information.

Some of the prejudicial material may be presented on a plate. The jury were shown intrusive surveillance video recordings of Dobson, Norris, Knight and Neil Acourt made in 1994. Reporting five years later, the Macpherson inquiry team very much doubted whether these recordings could have been put before a jury at a trial. But that was before the 2003 act allowed evidence of bad character to be admitted provided it had substantial probative value.

Dobson and Norris will be sentenced on Wednesday. Adults convicted of murder must be sentenced to life imprisonment. The judge must set a minimum term after which they may be considered for parole. In setting that term, the starting point in the case of a racially aggravated murder is 30 years. Without aggravating factors, it would be 15 years.

However, an offender who was under 18 when he committed murder must be sentenced to detention at Her Majesty's pleasure. Dobson was 17 and Norris was 16 in April 1993. Since they are now adults, they can expect to serve their sentences in adult prisons. But the starting point for an offender under 18 is 12 years, even if the offence is racially motivated.

Once a starting point has been set, the judge will increase the minimum term if there are aggravating factors (such as advance planning) and reduce the term if there are mitigating factors (such as a lack of premeditation) before arriving at a minimum period.