Exclusive: Channel 4 News learns that a Metropolitan Police detective was put under surveillance by News of the World journalists and his personal details targeted.
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The surveillance operation came during a crucial murder investigation which implicated private investigators who had alleged links to News International.
Channel 4 News understands Rebekah Brooks, then editor of the News of the World, was informed of the allegations by Scotland Yard at the time.
It was at a time when Rebekah Brooks - now one of the most powerful figures in the media industry - ran the tabloid News of the World and it was just three months after the alleged hacking into Milly Dowler's phone.
This is a story about a claim that Brooks was confronted by the police over allegations of her journalists targetting a murder detective. An astonishing story which at one point, we've been told, had the police secretly watching the News of the World watching the police.
Channel 4 News can reveal the story for the first time tonight.
At 9pm, 25 June 2002, BBC Crimewatch was about to announce yet another investigation into a notorious, unsolved murder.
The case involved the murder of Daniel Morgan, a private investigator who was found in the car park of a south London pub 24 years ago with an axe buried in his head.
The case collapsed again recently - for the fifth time - undermined hugely by police corruption in the early years. But it's what happened after this Crimewatch broadcast to the senior detective in charge, Dave Cook, which has never been told before.
Alastair Morgan, the brother of Daniel Morgan, the murdered private investigator spoke to Detective Dave Cook often during the investigation.
He told Channel 4 News: "Dave told me about it, he told me about it then but I didn't realise who the newspaper was at that point."
Within days of the Crimewatch broadcast, it's understood that Dave Cook had been told by colleagues he was being targetted by the News of the World.
Alastair Morgan describes what is supposed to have happened next: "I learned about the surveillance and then I learned that it was the News of the World that was carrying out the surveillance.
"Dave told me that he was out walking his dog, he was taking his dog for a walk one evening when he noticed a van in an odd location. I think he said behind some trees near his house. The following morning he noticed he was being followed."
It's alleged that the police discovered one of the vans was leased to the News of the World. So concerned were the police that a witness protection unit was mobilised - as well as a police counter surveillance team.
When finally confronted, the News of the World apparently said they were interested in whether Dave Cook was having an affair with a Crimewatch presenter Jacqui Hames. They were in fact married at the time. Jacqui Hames has told Channel 4 News she has been contacted by Operation Weeting Detectives investigating the phone hacking scandal.
What is so disturbing about this allegation is the timing of the targeting of Dave Cook. Because in the murder investigation he was leading, suspects in the case were private investigators who, it's alleged, had close links to the News of the World.
Channel 4 News also understands that Rebekah Brooks - now CEO of News International - knows all about this.
Because, it's claimed, there was a meeting at Scotland Yard in December 2002, in which the police challenged her over this.
We still do not know what the outcome of that meeting was, but both the News of the World and the Metropolitan Police appear never to have spoken about it publicly.
Tonight the News of the World told Channel 4 News: "News International has not been previously aware of these claims but will investigate any allegations that are put to them."
They say they are not in a position to confirm or deny whether any meeting took place or what may have been said if indeed a meeting did take place.