A bloodstain found on a jacket belonging to one of the men accused of murdering Stephen Lawrence was caused when the blood was fresh, the Old Bailey has heard.
The tiny stain, measuring 0.5mm by 0.25mm, was discovered on the collar of a jacket belonging to Gary Dobson by a cold case team.
Defence counsel argue that it was caused when an old, dried blood flake got on to the jacket via contamination and was dissolved during tests for saliva.
But forensic scientist Edward Jarman told a jury at the Old Bailey that his experiments suggested the stain was made by fresh blood.
He said that old fragments of Mr Lawrence's blood became "gel-like" during saliva testing and therefore would not soak into fabric.
Mr Jarman explained: "When these gel fragments were left to dry they became adhered to the fabric so when you touched them they stuck securely to it, but they had not absorbed into the fabric."
When he repeated the test using flakes made from fresh blood, they dissolved and caused a stain.
Dobson, 36, and David Norris, 35, are accused of being involved in the gang attack that killed Mr Lawrence in Eltham, south east London, in April 1993, which they deny.
Mr Jarman was part of a team at a company called LGC asked to help in a cold case review of Mr Lawrence's murder.
Earlier, the jury was told that he made key findings when he used sticky tape to gather debris from the original police evidence bag used to hold Dobson's jacket. Three fragments of blood were discovered, which had a chance of less than one in a billion of not being Mr Lawrence's blood.