Police have launched a fresh witness appeal after a woman's DNA was found near the spot where teenager Steven Lawrence was murdered 23 years ago.
Detectives recovered the new evidence from a bag strap found where the 18-year-old was stabbed to death in a racially motivated attack in Eltham, south east London on April 22 1993.
Improvements in forensic testing have allowed officers to identify the DNA of an unidentified female.
Detectives are investigating a possible theory the strap was used by the suspects as an "adapted offensive weapon".
Scotland Yard renewed their public appeal for information on the eve of what would have been Stephen Lawrence's 42nd birthday.
The black leather strap, which did not belong to Lawrence, is believed to have been left in Dickson Road, by the junction with Well Hall Road, near where he was attacked.
Chris Le Pere, senior investigator in the case, said: "So far we have been unable to identify the owner of the bag strap.
"While there is no evidence that a woman was at the scene of the attack, I need to establish who this bag belonged to, and why was it at the spot where Stephen was attacked."
A reconstruction and appeal for information about the owner of the bag will be shown on BBC's Crimewatch at 9pm on Monday.
Lawrence's father, Neville Lawrence, will also appeal for further information about his son's death.
"I am hoping that tonight's Crimewatch reconstruction, and the passing of time, will encourage people to come forward and assist us in determining the full circumstances of his death," Le Pere added.
Lawrence was stabbed to death by a group of up to six white men in an unprovoked racist attack as he waited at a bus stop in Well Hall Road with a friend.
In January 2012, Gary Dobson and David Norris were found guilty of being involved in the attack on Lawrence, and sentenced to life imprisonment.
Police are still trying to trace a man reportedly seen in a distinctive green jacket with a V emblem near Well Hall Road Roundabout at about the time Lawrence was attacked.
Anyone with information is asked to call the Met Police on 101 or Crimestoppers anonymously on 0800 555 111.