Jill Dando, who presented the Holiday programmed and Crimewatch, was shot dead on the doorstep of her Fulham home on 26th April 1999.
"The gunman considered taking lives to be all in a day's work and was paid handsomely"
The gun was reportedly broken into four pieces and thrown into a canal in Islington.
Barry George, Jill’s neighbour, was found guilty of her murder and jailed in July 2001 - but, after a retrial in 2008, he was found innocent and freed.
Now former police detective Mark Williams-Thomas, who famously exposed Jimmy Savile’s crimes, has said he believes that Jill Dando was assassinated because of her work on Crimewatch.
Speaking exclusively with The Mirror, he claims to have found an intelligence report naming two men from Islington, North London, who were said to be acting for one of the capital's biggest crime families
He said: “It suggested Jill was being targeted for investigating crime on television. The report goes on to detail how after shooting her the men disposed of the murder weapon in a canal on their home turf.
“My theory is that Jill was gunned down on the orders of a London underworld Mr Big to send out a direct, bloody message to others: ‘Do not take on organised crime.’”
He continued: "There are several reasons why I'm convinced a contract killer shot Jill. First, she was shot with a single bullet to the head which indicates they were well-trained enough to know that would be enough.
"I believe the gunman considered taking lives to be all in a day's work and was paid handsomely. He also got a buzz from pulling off the "perfect murder.
"A second major factor which supports the hitman theory is the fact that on a busy London street in broad daylight, no one saw the shooting or could even say for sure they had seen him. He just slipped away.
"Third, he vanished without a trace of DNA or any other evidence, bar the bullet."
He finished firmly: "I will pass my findings from the Dando Files to Scotland Yard and urge them to start a fresh investigation."
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