JURORS IN the Stephen Lawrence murder trial have been told they must acquit both defendants unless they are sure that scientific evidence allegedly tying them to the murder scene was not the result of contamination.
In his summing-up, Mr Justice Treacy warned the jurors that they must not base their decisions on emotion. He told the jury of four women and eight men that they must "reach verdicts on the basis of cool, calm consideration".
Lawrence, 18, was stabbed in a racist gang attack in Eltham, south east London in April 1993.
Gary Dobson, 36, and David Norris, 35, deny murder. According to their defence lawyers, the forensic evidence against them was contaminated.
The trial, which began at the Old Bailey last month, is now in its seventh week.
Although the court is normally closed throughout the Christmas week it has been specially opened during the holiday period for this case.
He set out the key questions that jurors must answer to reach a verdict.
The first question, he said, concerned the new forensic evidence relating to textile fibres, blood and hair, and whether jurors could be sure it came from Stephen Lawrence.
If so, they had to be sure it was not contaminated and if that could not be excluded, they must return a verdict of not guilty.
He also said that the jury then had to be sure that the defendants took part in the attack on the teenager, and if so, they intended to kill him or cause serious harm.
Under joint enterprise the two men can be convicted of murder if they did not inflict the killer blow, but if they knew someone in the group intended to cause serious harm.
The judge stressed they could take as long as necessary to reach a verdict.
The prosecution of Dobson and Norris followed the discovery of new forensic science evidence after a cold case review.