In that time the 27-year-old electrician did not appear to realise that a team of 30 Scotland Yard officers were following his every move.

Police were already staking out the redbricked block of flats in Scotia Road after the address had been found in documents left in one of the abandoned rucksacks from the abortive attacks last Thursday.

There was also partially destroyed evidence that the crop-haired bomber in the sweatshirt with a New York logo on the front, seen in CCTV pictures fleeing Oval station, had recently stayed at the Scotia Road property.

There are eight separate flats in the block. When Mr Menezes emerged from the communal front door just after 9.30am, the police must have realised from the photographs they carried that he was not one of the four bombers. Even so they decided that he was “a likely candidate” to follow because of his demeanour and colour, so one group set off on foot after him.

As he waited at a nearby bus stop the reconnaissance team sought urgent instructions on whether to challenge him right away or let him board a bus. They were worried about the dark, bulky, padded jacket he had zipped up on such a muggy morning.

The decision was taken to let him go, in the hope that he might lead his shadows to at least one of the bombers.

The bus journey was slow, as on any other Friday morning, but Mr Menezes seemed to be in no hurry. He was heading to Willesden Green to fix an alarm system. When it was obvious that he was getting off at the stop nearest Stockwell Tube station, the team on the bus alerted a three-man team of marksmen to move in.

As Mr Menezes waited to cross the busy main road, the decision was taken at Scotland Yard that he must not be allowed to get to the platform.

The marksmen were told: if you think he has explosives under his coat and he fails to heed shouted warnings, then you must shoot to kill.

As the three plain-clothes officers closed in on Mr Menezes, they say that they screamed their first warning that they were armed police. Their version is that he turned, ran into the station concourse, vaulted the ticket barriers and reached a waiting train before they could catch him. They shot him five times in the head when they believed that he was trying to trigger a bomb.

His cousin, Alex Alves, claims in one account that Mr Menezes was “playing around with a friend in a game of chase outside the station”.

The police insist that he was alone during the entire journey.

Another family member said that he had recently been attacked and robbed in that area by a gang of young white men and thought the plain-clothes officers were muggers.

By far the most controversial claim comes from a number of witnesses who have cast doubt on police statements that they shouted a warning or identified themselves to the suspect before opening fire.

Lee Ruston, 32, who was on the platform, said that he did not hear any of the three shout “police” or anything like it. Mr Ruston, a construction company director, said that he saw two of the officers put on their blue baseball caps marked “police” but that the frightened electrician could not have seen that happen because he had his back to the officers and was running with his head down.

Mr Ruston remembers one of the Scotland Yard team screaming into a radio as they were running. Mr Ruston thought the man that they were chasing “looked Asian” as he tumbled on to a waiting Northern Line train.

Less than a minute later Mr Menezes was pinned to the floor of the carriage by two men while a third officer fired five shots into the base of his skull.

Again, Mr Ruston says that no verbal warning was given.

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