The electrician was followed into the station by three unarmed surveillance officers, and down on to the train. Here, the account of the officer codenamed Hotel Three becomes crucial. He admits being told to allow Mr de Menezes to enter the station, and then following him on to the train. Both men sat down. Some 15 seconds later, Hotel Three saw armed police officers walk on to the platform, so he went to the carriage doors, blocked them open and shouted out: "'He's here' and [I] indicated to the male in the denim jacket with my right hand. I then heard shouting which included the word 'police' and turned to face the male in the denim jacket.
"He immediately stood up and advanced towards me and the SO19 officers. He appeared agitated and I noticed that his hands were held below his waist and slightly in front of him. The man did not stand still and advanced to within about three or four feet of myself and the SO19 officers. Assessing that I may be dealing with a terrorist subject and fearing for the safety of the public on the carriage the SO19 officers and myself, I grabbed the male in the denim jacket by wrapping both my arms around his torso, pinning his arms to his side. I then pushed him back on to the seat where he had previously been sitting with the right-hand side of my head pressed against the right-hand side of his torso. At this stage his body seemed straight and he was not in a naturally sitting position. I then heard a gunshot very close to my ear and was dragged away on to the floor of the carriage."
From this evidence, a critical question emerges - one that raises doubts about the secret rules known as Operation Kratos which allow the police to "shoot to kill". If he was a suspected suicide bomber, why was he allowed to board a train?
The IPCC dossier reveals that critical operational errors may have been made. The report states that the firearms unit were allowed to use "unusual tactics" if they "were deployed to intercept a subject and there was an opportunity to challenge, but if the subject was non-compliant, a critical shot may be taken". So why, the IPCC is asking, was Mr de Menezes not intercepted or given the chance to surrender?
Other police disclosures add to the concerns. One officer stated: "The current strategy around the address was as follows: no subject coming out of the address would be allowed to run and that an interception should take place as soon as possible away from the address trying not to compromise it." So what went wrong?
The IPCC investigation is now turning to the most senior officers on duty that day - Assistant Commissioner Alan Brown, known as Gold Command, and Commander Cressida Dick, the Met's most senior woman officer and the officer in operational command that morning - and the orders they gave. Claims last week that Commander Dick had specifically ordered the police not to shoot are denied by sources at Scotland Yard. But nor, it now seems, did she give specific instructions to "shoot to kill".
The IPCC dossier states that once Mr de Menezes was wrongly identified as a suspect, "Gold Command made the decision and gave appropriate instructions that de Menezes was to be prevented from entering the Tube system. At this stage the operation moved to code red tactic, responsibility was handed over to CO19 [the Met's specialist firearms unit]."
Sir Ian Blair is also expected to be interviewed by the IPCC - believed to be the first time a Met commissioner has been formally questioned for alleged policy failures. This will heighten an intensifying political battle between the IPCC, the victim's family and the Met, a battle which pits old foes against each other. The commission is run by two prominent human rights activists - its chairman, Nick Hardwick, the former chief executive of the Refugee Council, and deputy chair, John Wadham, former head of the civil rights group Liberty.
And the family, to the private irritation of the police, is being represented by Gareth Peirce, the most experienced and successful civil rights lawyer of her generation who is notorious in police circles for acting for IRA bombers and alleged Islamist militants. The family's spokesman is Asad Rehman, an experienced anti-racist activist who joined George Galloway's campaign team after leaving Amnesty International.
The row over Mr de Menezes' death is threatening to cause diplomatic damage to Britain's relations with Brazil. In the aftermath of the shooting, Brazil's left-of-centre coalition, dominated by the Workers Party, played down the tragedy. The family's lawyers allege that government officials urged the family not to pursue a claim for compensation and successfully persuaded Mr de Menezes's parents, Maria Otoni de Menezes and Matozinho Otoni da Silva, not to order a second post mortem. But last week's revelations put the Sao Paolo coalition government under intense pressure. It has sent two senior legal investigators - a federal deputy attorney general and federal prosecutor - to London to meet the IPCC and senior Met officers.
The outrage in Brazil has prompted a few off-the-record remarks from British politicians, given the level of gun violence over there. In June, a Unesco study revealed that 550,000 Brazilians have been killed in firearms incidents since 1979, and that in 2003, one in three deaths of Brazilians aged 15-24 were attributable to guns. In the first eight months of 2003, police allegedly shot dead 800 civilians in Rio de Janeiro alone.
But last week, the London shooting dominated Brazil's attention in a way that killings at home seldom do. Sir Ian Blair may have wished that the row remained far away. It did not. Amid calls for his resignation, he was forced to give hasty interviews in which he apologised for the incident, but pointed out that 56 people had died in the London bombings and that, in effect, Mr de Menezes was a casualty of war. It remains to be seen if the career of Sir Ian Blair will be, too.