Stephen Lawrence trial: Forensic scientist challenged
The evidence of a forensic scientist in the Stephen Lawrence trial has been challenged by a defence barrister.
Edward Jarman told the Old Bailey he had found a "microscopic" blood-stain from the teenager on a jacket removed from the home of defendant Gary Dobson.
But Tim Roberts QC, for Mr Dobson, said the science was unproven and urged caution over such a "tiny" stain.
Mr Dobson, 36, and David Norris, 35, deny murdering 18-year-old Mr Lawrence in Eltham, south-east London, in 1993.
The prosecution alleges they were part of a group of white youths that shouted a racist remark before forcing Mr Lawrence to the ground and stabbing him twice.
Mr Jarman told the court that a single blood-stain measuring half a millimetre, found on a jacket associated with Mr Dobson, was most likely to have come from Mr Lawrence.
He said: "It's very difficult to measure fragments of blood on such a tiny scale but we've suggested that the total volume could be possibly less than a couple of microlitres (cubic millimetres)."
Tim Roberts QC, for Mr Dobson, told the court that the bloodstain was so tiny, and the methods used to analyse it so unique, that any interpretation should be treated with caution.
Cross examining Mr Jarman, Mr Roberts asked him why there was no other blood-staining on the jacket if the mark on the collar had been caused by fresh blood.
He said: "If it's all landed at the same time in the same place in the same circumstances, why hasn't it all behaved in the same way and soaked into the weave?"
Mr Jarman replied: "It wouldn't necessarily all soak in, depending on the actual nature of the stain, of the blood and what it's made up of."
The defence claim that the stain was caused when a dried blood flake dissolved during saliva screening.
Mr Jarman accepted that around 40 blood fragments had got on to the front of Mr Dobson's jacket while it was being tested for saliva.
However, he told the court that he did not believe this process caused the stain on the collar.
"It appears to have soaked into the weave," he said.
The court has heard that Mr Jarman's testing found the saliva screening process caused blood to become gel-like and did not produce a stain.
The scientist, who specialises in body fluids, devised his own experiments to determine the effect of the saliva tests.
Mr Roberts told him: "You were on a limb with this leading-edge evaluation."
Mr Jarman replied: "Yes, aspects of this are new, I suppose."
The defence claims forensic evidence, found in 2008 in a cold case review allegedly linking Mr Dobson and Mr Norris to the killing of the black teenager, resulted from contamination.
The prosecution says tiny amounts of blood, fibres, and hair found on clothes taken from their homes prove their guilt.
Testing for blood carried out on a cardigan seized from Mr Dobson's house, and jeans, a sweatshirt and another cardigan taken from Mr Norris's home were inconclusive.
The jury was shown photographs of a boy wearing a sweatshirt and jeans which the defence maintains are those seized from Mr Norris's house.
Mr Jarman said he was unable to say whether stains on the jeans were the same as those on the pair he examined forensically.
He told the court he had not considered the possibility that traces of DNA found on the trousers could have come from one of Mr Norris's brothers.
The trial was adjourned until Friday.