An appeal to the criminal world for leads on the illegal handgun used to murder BBC presenter Jill Dando has been made by police.

Ms Dando, 37, who presented Crimewatch UK and Holiday, was shot outside her house in Fulham, west London, on Monday at 1130 BST. Police said a 9mm semi-automatic pistol was fired once at the side of her head from close range.

Detective Chief Inspector Hamish Campbell, leading the inquiry, said: "Somebody must know if they recently provided such a weapon to somebody through the illegal network. We still need to hear from them."

The BBC's George Eykyn: "The search goes on"

The make of the gun was likely to have been a Browing or a Tanfoglio, which were banned after the Dunblane massacre when Thomas Hamilton gunned down 15 children and their teacher in 1996.

Criminologist Kate Broadhurst, of Leicester's Scarman Centre for the Study of Public Order, said: "This is the weapon of the drug dealer and the professional criminal."

New witness

A witness who may have come face to face with Ms Dando's killer on Gowan Avenue has come forward. The 10-year-old boy was being driven to school by his mother when he saw a "weird" man loitering just outside her home.

Cmdr Brian Edwards and DCI Hamish Campbell explain the circumstances of the killing

He and his mother went straight to the police from their south-west London home after hearing of the death on television.

The boy said he had seen a man in an old-fashioned suit and a checked cap pacing the pavement on Gowan Avenue in such a distracted state that he almost walked in front of their car. He has been able to draw pictures of the suspect's clothing for police.

"I thought he was going to walk into the road and I got mum to beep at him," he said. "He looked at the car and that is when I got a look at him. I did not see his face, it was a quick flash and he turned back."

Speculation that a professional hitman was involved increased after the execution-style manner of the killing was revealed, but police are keeping an open mind.

At least seven witnesses who could have seen the man have come forward.

Detective Chief Inspector Campbell said a window cleaner had seen a man outside Ms Dando's home at about 1030 BST.

He is described as being in his late 30s or early 40s, 5ft 11in tall, dark haired and wearing a suit.

Psychologist Oliver James: "This is completely bizarre in the history of murder"

An hour later and just before the shooting another witness saw a similar man, wearing large black-framed spectacles which appeared too large for him.

Ms Dando, who had gone shopping in Hammersmith Mall after leaving her fiancé's home in Chiswick at 1000 BST, was shot just after arriving home.

Police said that after the killing, a man with a mobile phone had been seen running away from Ms Dando's home towards Putney Bridge, where two witnesses saw a man climbing railings at Bishop's Park, next to the River Thames.

The BBC's James Helm: "The police are not ruling anything out"

A man sweating profusely was later seen at a bus-stop in Fulham Palace Road, but he is not thought to have got on a bus.

Ms Dando's murder prompted tributes from the Queen and Prime Minister Tony Blair.

BBC News Online received more than 9,000 e-mails from users wanting to remember the star in the hours following her death.