In a nondescript office at the London headquarters of the Crown Prosecution Service (CPS), a member of its special crime division has spent the past four weeks poring through pages of evidence detailing the blunders that led police to gun down an innocent man.
The level of secrecy surrounding the investigation is so great that the CPS will not even officially release the name of the lawyer who will decide if officers should be prosecuted over the killing of 27-year-old Jean Charles de Menezes at Stockwell Tube station last year.
Senior CPS sources, however, have confirmed that the report presented to them by the Independent Police Complaints Commission (IPCC) last month does allege that police tried to fake evidence relating to the killing.
This allegation, that Special Branch officers involved in the bungled operation tried to implicate their own colleagues in his death by altering an official log, is now central to the case against police.
It is the most damning charge so far facing the Metropolitan Police who are already bracing themselves for the outcome of the CPS investigation which is expected to conclude this Easter. Sir Ian Blair, the Metropolitan Police Commissioner, is already the subject of a separate inquiry by the IPCC over allegations that he misled the public in the hours after Mr de Menezes was gunned down by firearms officers.
MPs and human rights groups have also widely criticised the controversial shoot-to-kill guidelines, used to "execute" 27-year-old Mr de Menezes, which advise officers to fire into the head of suspected suicide bombers to prevent them detonating a bomb.
On the day that Mr de Menezes died, a team of surveillance officers had been sent out to hunt down Hussain Osman who was allegedly involved in the failed suicide bombing on the tube the previous day.
They were instructed to stake out an address in South London which had been found on a piece of paper in the wreckage of one of the abortive bus bombings.
One of the residents living in the block of flats where they were sent happened to be Mr de Menezes, who was spotted coming out of the block by the undercover officers.
It has now emerged that, according to the IPCC report, one of the team wrongly identified the Brazilian electrician as Hussain Osman and as a result firearms officers were dispatched to stop him.
Once they realised that an innocent man had been killed, the police log was altered so that instead of reading "it was Osman", the records were changed to say "it was not Osman".
The surveillance officers are understood to have denied being involved in making the changes. But police could now be prosecuted for perverting the course of justice. However, it is unlikely that the officers involved in the cover-up will face manslaughter charges, which would bring huge embarrassment to the Met which is struggling to protect its image.
CPS sources have told The Independent on Sunday that their aim is to ensure they do a thorough job in establishing who is to blame for the killing of Mr de Menezes.
But they admit they are under huge pressure both from those who want to see the police prosecuted and those who argue that individual officers are being scapegoated.
As one told the IoS: "It is a case of damned if we do and damned if we don't."
The Brazilian government has already warned it expects somebody to be held accountable for the shooting of Jean Charles de Menezes.
A high-level delegation, which visited this country earlier this month, said they may take the case to the European Court of Human Rights if it does not go to the British courts.
The de Menezes family, who want the police to be punished, have demanded a public inquiry into the shooting because they say that is the only way that the truth will emerge as to how their relative died. They are angry that they have not yet been allowed to see a copy of the IPCC report which has been seen by the Met as well as by Charles Clarke, the Home Secretary.
However, one former firearms officer said that the public could never be able to comprehend how much pressure the firearms officers were under on the day that Mr de Menezes was killed.
The source said: "The circumstances were absolutely unprecedented. There had been another attempt to blow up the Tube and there was a suicide bomber on the run. The officers who pulled the trigger thought they were stopping commuters being blown up. No one can imagine how devastated they would have been."Reuse content