They have compiled a list of 400 names in connection with the fatal shooting of Miss Dando on her doorstep in Fulham, west London, in April.

The BBC's Crime Correspondent Stephen Cape reports: "It's a mamouth task"

Two hundred people have now been struck off and another 120 others are being treated as low priority.

Those under investigation include about 50 fans who wrote to the presenter at the BBC in the months before her death.

Police still assume killer was an obsessive fan

But detectives are certain that she was not stalked or subjected to any other physical harassment.

The most obsessed fans, some of whom wrote to her nine times, have already been eliminated from enquiries.

Detectives said they were typically single men in their late 20s or 30s. Some had decorated their homes with pictures of the presenter.

Still no motive

They are now checking out everyone else who wrote repeatedly to the presenter, as well as people named as potential suspects by members of the public, and friends and acquaintances of Miss Dando.

Ten of Miss Dando's former boyfriends have also been ruled out of carrying out the shooting.

But detectives are also investigating whether any of the suspects could have been involved in a conspiracy to commit the murder, although they have not yet established a motive for the attack.

It is still assumed that the presenter was the victim of an obsessive fan, or a contract killing.

Vehicle appeal

Detectives have focused their investigations on the last two years of her life, as they believe they are most likely to provide an explanation for her death.

The 486 people listed in her Filofax are being checked out.

Scotland Yard has also launched a new appeal for information about the murder, and are offering a £250,000 reward.

Detective Chief Inspector Hamish Campbell appealed for information about any vehicles linked to the crime and details about the weapon used.

Anyone with information is urged to call the incident room at Kensington Police Station on 0181 246 0732 or Crimestoppers on 0800 555 111.