Undercover police officers who stole into the premises of Southern Investigations Ltd armed with state-of-the-art bugging devices were under no illusions about the need to ensure that no trace should be left of their visit to the drab private investigator's office on a south London high street.
The team from Scotland Yard's anti-corruption unit were conducting Operation Nigeria, an inquiry begun early in 1999 into the activities of Jonathan Rees, the portly owner of the detective agency who was a suspect in the murder 12 years earlier of his business partner, Daniel Morgan.
The second aim of the investigation was to gather information on Rees and his network of contacts, including bent serving police officers, dedicated to obtaining information, often illegally gathered, for sale to a number of keen and often insatiable customers: newspapers.
An internal police report made clear the calibre of Rees and his accomplices: "They are alert, cunning and devious individuals who have current knowledge of investigative methods and techniques which may be used against them. Such is their level of access to individuals within the police... that the threat of compromise to any conventional investigation against them is constant and very real."
The bug planters nonetheless did their work well. Over the next seven months, detectives chronicled Rees's dealings with a number of Fleet Street titles, including the News of the World, as he provided a steady stream of stories and tit-bits from his contacts.
It was a lucrative trade. Rees was recorded complaining that he was owed £12,000 by one tabloid, but his company's biggest customer was the NOTW, paying up to £150,000 a year. As the private investigator put it: "No one pays like the News of the World do."
Using his roll-call of informants, including bank employees and even a VAT inspector susceptible to bribes, Rees offered his clients the inside track on the arrest of the M25 murderer Kenneth Noye and the sex lives of Buckingham Palace servants.
By September 1999, Operation Nigeria had gathered little evidence on the death of Mr Morgan, but it had recorded Rees plotting to frame Kim James, a former model, by having cocaine planted in her car to allow her estranged husband to win custody of their child. Rees was convicted of the conspiracy at the Old Bailey and sentenced to six years' imprisonment, increased to seven on appeal.
With the stain of a conviction for conspiracy to pervert the course of justice on his record, it might have been assumed that his previous clients in the press would resolve to steer clear of him when he was released in 2004. And so they did – apart from the NOTW. Rees began providing information to the title again in 2005 under the editorship of Andy Coulson. The relationship ceased in April 2008 when Rees was charged with Mr Morgan's murder.
But despite the desire of the Yard to send a message that any involvement of journalists with police corruption would not be tolerated, no reporter who dealt with Rees has been arrested or charged. Following Operation Nigeria, the CPS decided there was no evidence that journalists knew the private investigator's information was obtained illegally.
In March this year, Rees was acquitted of the gruesome killing of Mr Morgan, who was found in a pub car park with an axe embedded in his head. The murder remains unsolved.