A witness who may have seen the killer of student Marsha
McDonnell has come forward, following a BBC Crimewatch reconstruction.
Police have linked two other attacks to Marsha's murder
The potentially crucial witness is to help detectives create an e-fit of the man she saw.
The new lead came as Marsha's family announced that her funeral is to be held on Friday.
Marsha, 19, was killed near her home in Hampton in the early hours of 4 February after a night out with friends.
Detectives are also looking at about 10 possible suspects for the murder and two linked attacks on a 17-year-old girl and an 18-year-old youth in south-west London.
Four weeks earlier the new witness had seen a man standing over the 17-year-old girl as she lay on the ground, a mile away in Strawberry Hill.
The girl woke up with head injuries in hospital and it was initially assumed she had slipped on ice, as she could not remember being attacked.
But her family reported the incident to police following the death of Marsha McDonnell.
A few weeks after Marsha's death an 18-year-old boy was attacked by a hooded man who lunged at him with a blunt instrument in nearby Hampton Hill - the boy escaped unhurt.
The three attacks took place within a mile of each other and police believe the same man is responsible for them all.
A Scotland Yard spokesman said: "Officers investigating the murder of Marsha McDonnell and other attacks in the Hampton area have identified an important witness through Crimewatch UK."
A statement from the McDonnell family said they would like to see "as many of Marsha's friends as possible" at the 7 March funeral, which is being held in the London area.
Shane McDonnell, Marsha's uncle, said: "We want to gather and celebrate the beautiful life she had and remember all the joy and happiness that Marsha brought us."