Jean Charles de Menezes was the victim of "terrible and extraordinary circumstances", the senior British policewoman in charge of the operation that led to his death told an inquest today.
Deputy assistant commissioner Cressida Dick insisted that none of the officers involved did anything wrong, however.
Ms Dick listed a series of "unfortunate" coincidences as she gave evidence to the inquest into the shooting of the innocent Brazilian electrician.
These included: the fact that he lived in the same block of flats as failed July 21 suicide bomber Hussain Osman; the fact that he looked "very like" Osman; the fact that the first surveillance officer was "indisposed" and only got a short glance at him; Mr de Menezes's innocent behaviour in getting off and then back on a bus; and the fact that he entered the Tube station used by three of the July 21 bombers the previous day.
Mr de Menezes, 27, was shot seven times in the head at Stockwell Tube station in south London on July 22, 2005 by police marksmen after being mistaken for an on-the-run terrorist.
Ms Dick led the Scotland Yard control room overseeing the pursuit of the Brazilian by surveillance and firearms officers who feared he was Osman.
Asked what went wrong, she told the inquest: "One thing that clearly went wrong was that we as a nation did not manage to prevent those attacks on July 7 or indeed Hussain Osman and others' attacks on the 21st.
"Mr de Menezes was the victim of some terrible and extraordinary circumstances the day afterwards.
"He was extraordinarily unfortunate to live in the same block as Hussain Osman had been, he was desperately unfortunate to look very like Hussain Osman.
"There are some things that happened - for example the fact that the first surveillance officer was indisposed and only able to get a relatively short glance.
"Mr de Menezes waited only a very short time at the bus stop so - as I understand it today, I didn't know that at the time - therefore a surveillance officer again would not have a great ability to look at him properly.
"Some of the things that Mr de Menezes did in all innocence - the way he behaved, the way he came off the bus and on the bus - contributed to my assessment of him as a bomber from the day before, and someone who might be intent on causing an explosion today.
"And finally the thing I would say last is he had the great misfortune of entering the same Tube station that three of the bombers had entered the day before.
"So lots of things happened, any one of those you might describe as going wrong."
But the senior officer added: "If you ask me whether I think anybody did anything wrong or unreasonable in the operation, I don't think they did."
Ms Dick was watched in the courtroom at the Oval cricket ground by the shot Brazilian's mother, Maria Otone de Menezes, who attended the hearing for the first time today.
Ms Dick described Mr de Menezes's death as "an awful tragedy".
The inquest also heard that she went to the wrong room and missed the start of an important meeting of senior police officers to discuss strategy on the morning of the shooting.
On July 22, 2005 Ms Dick arrived early at New Scotland Yard and went to a room on the 16th floor in time for the 7am conference.
But 10 minutes later she received a call to tell her she had been sent to the wrong place and should have been on the 15th floor.
Asked who was present when she arrived at the meeting at 7.15am, she said: "I don't think they were all there. It certainly was a meeting in which people came and went.
"I had the feeling that it might have been going on for some time before I was there."
Ms Dick also told the inquest she was Scotland Yard's most experienced commander of high risk firearms operations in the years before Mr de Menezes's shooting.
After five years with Thames Valley Police, she returned to the Met in 2001 and became a commander in the force's specialist crime directorate with responsibility for organised crime, gun crime and hostage-taking across London.
Ms Dick said between 2003 and 2007 she was involved in overseeing serious firearms operations "literally on a daily basis".
She said: "I think I probably had the highest volume under my command by far of the most high risk and complex firearms operations."
Mrs de Menezes, 63, flew into Britain from Brazil with her older son, Giovani de Menezes, 36, on Friday.
Although this was the first day they have attended the inquest, other family members have been present since the hearing began on September 22.
Listening to a Portuguese translation of the proceedings on headphones, the dead man's brother tutted and shook his head as Ms Dick outlined her version of what went wrong in the operation.
The inquest has heard that the officer in charge of the hunt for the July 21 bombers ordered that everybody coming out of an address linked to Osman should be stopped on the morning of July 22.
But it turned out that the address - 21 Scotia Road in Tulse Hill, south London - was part of a block of flats with a communal entrance.
Ms Dick said she was made aware that people had left the block and not been stopped because surveillance officers did not know which flat they came from.
She described this decision as "perfectly sensible", adding: "A lot of people are going to be coming out probably at that time in the morning.
"If you take your surveillance officers and ask them to follow everybody who comes out of the block, you are very very soon going to end up with no surveillance officers.
"You are going to risk stopping people who know absolutely nothing about number 21, aren't able to provide you with good intelligence, and I felt that was going to lose us our resources very quickly."
Mr de Menezes was followed by surveillance officers after he emerged from the Scotia Road block of flats, where he was living at the time, at about 9.34am.
He was shot dead 32 minutes later after being allowed to get on board a London Underground train at Stockwell Tube.
Mrs de Menezes left the courtroom in tears after hearing details of the build-up to her son's death.
She was ushered into a private room having being led away arm-in-arm with a Justice4Jean campaigner.
Ms Dick asked the surveillance team following Mr de Menezes to tell her how confident they were he was Osman in percentage form, the inquest heard.
Coroner Sir Michael Wright asked her: "May we infer that as far as you were concerned, you were short of a positive identification?"
The senior officer replied: "It's a very common question to ask. It is extremely unlikely in such a fast-moving thing to get 100%.
"This team haven't had very long looking at this person, they have not seen him before, they don't know him.
"But whatever answer I had got would have informed my decision-making."
She added: "Was it at that stage positive? I don't think I could describe it as that."
In the event she never did receive a reply to her question, the inquest jury was told.
But while Mr de Menezes was still on a bus from Tulse Hill to Stockwell, senior firearms commander Detective Chief Inspector Greg Purser told Ms Dick: "They're certain it's him".
Ms Dick denied she gave an order that Mr de Menezes must be stopped from getting on to a train at Stockwell "at all costs".
Retired Special Branch detective Mark Lewindon told the inquest on Friday he believed she used these words.
But asked today whether she said this, Ms Dick replied: "No, I did not."
Ms Dick also denied she instructed the firearms teams to use lethal force to stop Mr de Menezes.
She said: "I would need to be absolutely satisfied that this person posed a dreadful imminent threat to members of the public before I would order a critical shot."
The senior policewoman added: "I was asking for what you might call a conventional - albeit aware of all the risks - challenge from the firearms officers."