Police have uncovered new witnesses who saw a man fitting the description of their prime suspect loitering in the area in the days leading up to her murder.
Senior officers investigating the case are understood to believe that Miss Dando's killer secretly watched her home for several weeks before shooting her.
Police have uncovered new witnesses who saw a man fitting the description of their prime suspect loitering in the area in the days leading up to her murder.
The suspect is a smartly-dressed man in his thirties or forties with dark hair, a Barbour-style jacket over a blue suit who used a mobile phone.
He has been described as looking "like an estate agent".
At least two neighbours saw him in the area within about 90 minutes of the murder, according to reports.
TV appeal
Detectives suspect that could have been part of a plan to make an attempt to introduce himself to the 37-year-old television presenter, who was selling her house in Fulham, south-west London at the time.
It is reported that in the run-up to Miss Dando's death, he may have communicated with her, perhaps by letter, and was rebuffed.
Another theory, apparently favoured by Miss Dando's fiance Dr Alan Farthing, was that she was executed by a stalker who could not cope with the idea that she was soon to marry.
Officers have not ruled out the theory that she was the victim of a contract killer but no one has come forward with credible information, despite a £250,000 reward.
Detectives are expected to reveal the new clues on Crimewatch on Wednesday in an appeal to mark the first anniversary of her death on 26 April.
They believe the killer will be watching and the officer leading the investigation, Detective Chief Inspector Hamish Campbell, will make a personal appeal to him to give himself up.