Forensic evidence clinched case

13 April 2012

The prosecution hinged on tiny traces of forensic evidence found by a cold case team.

This involved months of painstaking examination and testing by staff at private company LGC, including viewing every inch of any exhibit linked to a suspect with a microscope.

Here are their key findings:

Blood:

Edward Jarman, a forensic scientist who specialises in body fluid analysis, carried out testing for blood, saliva and DNA on items of clothing seized from the suspects' homes.
In the debris from the original evidence bag holding Gary Dobson's jacket, the team found three blood fragments which had less than a one in a billion chance of not being Stephen Lawrence's.

Another blood fragment which had encased three fibres and matched Mr Lawrence's DNA to the same probability was also discovered, although only a partial profile for DNA testing was obtained.

When Dobson's jacket was examined all over with a low-powered microscope, a tiny bloodstain measuring 0.25mm by 0.5mm was found on the collar. This matched Mr Lawrence's DNA profile to the same probability.

The defence argued that the stain had been caused by saliva testing, however Mr Jarman found that when old flakes of Mr Lawrence's blood were exposed to a chemical used in the testing they became "gel-like". They did not cause staining and would not absorb into the fabric.

He maintained that the most likely cause of the stain was "primary transfer", meaning that it was caused by wet blood shed during the fatal attack.

Fibres:

Fibres expert Roy Green and his colleagues microscopically compared tiny fibres found on exhibits and used a machine to scientifically measure their colour.

The rarity of fibres was partly quantified by how often they occurred in a Home Office database compiled in the 1980s.

The team found a total of 16 fibres linked to Mr Lawrence's clothes on tapings - where sticky tape is passed over the garment - from Dobson's jacket and its original evidence bag.

These included four rare red-orange polyester fibres and seven quite common pink-orange fibres that matched Mr Lawrence's T-shirt - one of which appeared to be bloodstained. There were also two quite rare blue-green acrylic fibres which matched Mr Lawrence's jacket.

In debris from the original packaging of Dobson's jacket there was one red-orange fibre matching Mr Lawrence's T-shirt and a fragment of blood that contained two quite rare blue acrylic fibres that matched his cardigan.

Seven fibres were found on tapings from a sweatshirt seized from David Norris' house - six from Mr Lawrence's trousers and one from his T-shirt.

Hair:

Hairs specialist Deborah Hopwood told the court that a number of short, cut fragments of hair were found on sticky tape passed over Mr Lawrence's outer clothes.

The team then discovered two tiny hairs among debris recovered from the Norris jeans - one of which was 1mm long and appeared to be bloodstained at one end. It was too small to send for DNA analysis.

The other was 2mm long and was sent to the United States to be tested for mitochondrial DNA. This is a short DNA sequence inherited from the mother and shared with anyone in the maternal line of a family.

The hair had the correct profile for the maternal line of Mr Lawrence's family. It could not be tested for nuclear DNA because the hair had no root.

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