"We will solve this," Detective Inspector Ian Horrocks, on the inquiry team based at Kensington police station, told BBC News Online.

"There would be no point in putting time and effort into the inquiry if we weren't confident of success."

But he stressed that, like many murder inquiries, it would take time and he was not prepared to go into any details about the current investigation or give a specific reason for his optimism.

Jill Dando: A murder that shocked the nation

Ms Dando was shot in the head on the doorstep of her home in Fulham, west London, on 26 April.

Since then, several witnesses have come forward and a photofit has been issued of a man seen "sweating profusely" at a bus stop near Gowan Avenue, where Ms Dando was killed.

In the last few weeks there have been no significant new leads - at least none that have been made public - in spite of a reconstruction shown on Crimewatch, the BBC One programme that Ms Dando used to co-present.

Newspaper reports dismissed

Naturally, the dearth of information has sparked rumours as to the motive for the mysterious killing.

Last weekend, the Sunday Mirror reported that a "source" had told them undercover police were staking out a pub in Birmingham where members of the criminal underworld were believed to have sold a gun to Ms Dando's killer.

But Det Insp Horrocks dismissed this, and other reports where there was no named source for the information.

He pointed out that the murder weapon - believed to be a 9mm "short" automatic - has still not been found.

He also said detectives were still keen to trace the man seen at the bus stop on Fulham Palace Road on the day of the murder.

Photofit of man at bus stop

But he did add that police were still interested to hear from or about anyone in the area of Gowan Avenue on the day of the murder.

"If people have got specific information about the gun or the event itself, we would want them to contact us," he said, adding that people were still coming forward with information about the murder.

It is hoped that The Daily Mail newspaper's offer of £100,00 for information leading to the capture of the murderer and Crimestoppers' £50,000 reward will encourage more people to contact police.

So far, police have only arrested one person after an anonymous tip-off. He was released on bail on 28 May.

It emerged later that the man questioned was funeral director James Shackleton, known to police as a hoaxer who had been arrested and released over other high-profile murders such as the Rachel Nickell case.

"This man is of no interest to this inquiry," said Det Insp Horrocks, who added that the police had a duty to follow up all possible leads no matter how dubious they seemed.