The Metropolitan Police was today found guilty of breaching health and safety laws over the shooting of innocent Brazilian Jean Charles de Menezes.
The 27-year-old died following a "catastrophic" series of errors in the operation which ended in his death.
He was shot seven times by specialist firearms officers at Stockwell Tube station after being mistaken for failed suicide bomber Hussain Osman.
Prosecutors at the Old Bailey set out 19 alleged failings in the police operation in the hours leading up to the shooting on July 22, 2005.
The jury convicted the force on the second day of its deliberations.
Metropolitan Police Commissioner Sir Ian Blair, who faced immediate calls to resign, was in court to hear the verdict and sentence.
The force was fined £175,000 and ordered to pay £385,000 costs by trial judge Mr Justice Henriques.
The judge told the court: "This was very much an isolated breach brought about by quite extraordinary circumstances.
"One person died and many others were placed in potential danger."
The judge said he hoped further necessary lessons would be learned. The judge added: "In sentencing I shall not lose sight of the fact that this was a unique and difficult operation."
But he said a heavy fine would result in a loss to the public purse and reduction in essential policing."
In a rider to the verdict, the jury cleared the officer in charge of the operation which led to the shooting, Cressida Dick of personal responsibility.
The foreman told the court: "In reaching this verdict the jury attaches no personal culpability to Commander Dick."
The judge said he agreed with the juries rider about Ms Dick.
Ronald Thwaites QC, representing the Met, had told the jury Mr de Menezes was acting in an "aggressive and threatening manner" when challenged by officers.
But campaigners reacted angrily to the way police defended the case, accusing them of a "sickening" attempt to blacken Mr de Menezes's name. There was also a bitter courtroom battle over prosecution claims that a composite image of the Brazilian victim and Osman, produced by the defence, had been doctored to make them look more alike.
The trial and investigation is estimated to have cost around £3.5 million in public money. But it was nearly derailed after an armed police raid on the home of a juror's ex-boyfriend in the second week of the case, in which the female juror's baby was taken away.
Sir Ian Blair, whose office was on trial during the case, said before it started that he feared a guilty verdict would have a "profound" impact on policing throughout the UK.
During the trial, prosecutors claimed that "fundamental failures" at all levels led to the death of Mr de Menezes.
Police were unsure if he was in fact Osman but still allowed him unchallenged onto two buses and a Tube train.
Surveillance officers who were following him asked their Scotland Yard control room more than once if they should arrest him but were told to wait for the arrival of SO19 firearms officers.
Deputy Assistant Commissioner Dick denied claims that she missed the "one safe opportunity" to stop him and that she lost control of the operation.
She said she was told five times that the man police were following was Osman.
Mr de Menezes was followed from a block of flats at Scotia Road, Tulse Hill, south London, that was linked to Osman. The surveillance operation at the block was launched at 4.55am but SO19 officers had still not arrived four hours later when Mr de Menezes, an electrician, left on his way to work.
An officer who was meant to identify him as he came out of the communal doors was unable to do so as he was "relieving himself", the court heard.
It was also alleged that there was a "noisy and chaotic" atmosphere in the 16th floor control room which "cannot have helped" the decision-making process.
Surveillance and firearms officers whose identities are protected and who the court was told "live in the shadows" gave evidence to the trial under assumed names and behind screens.
One of them, firearms team leader Ralph, broke down in court as he defended the actions of his men, who ran down into the station after the man they believed was a suicide bomber.
"Despite the outcome, I was very proud of them," he said.
Ralph, who was in charge of the SO19 "black team", said he was told over the radio that the man being pursued was "our man" and was acting "nervous and twitchy".
The court heard that the firearms officers were issued with highly deadly "dum dum" bullets and told that they might have to use "new and unusual tactics" and "might have to shoot someone point blank in the head".
However, the "Kratos" command for dealing with suspected suicide bombers by shooting them dead without warning was never issued, the Old Bailey was told.
A surveillance officer, known as Ivor, told how he followed Mr de Menezes into the Tube carriage, grabbing him and pinning him to his seat when he realised firearms officers were there, and shouting: "Here he is."
The innocent Brazilian was then shot five times in the head, once in the neck and once in the shoulder, by two SO19 officers.
Jurors saw CCTV footage of the marksmen, codenamed C2 and C12, heading down the escalator into the station, but they did not give evidence.
The court was also shown pictures of Mr de Menezes after the shooting, lying dead on the floor of the Tube carriage.
Mr Justice Henriques told the jury that the police were not "above the law".
But Mr Thwaites said a conviction would have the effect of "putting handcuffs on the police". He said the prosecution should never have been brought and that Mr de Menezes was acting like a suicide bomber when he was shot.
The jury heard evidence that Mr de Menezes had taken cocaine and had a forged stamp in his passport.
Mr Thwaites even accused the judge of bias, claiming his summing up had been "entirely pro-prosecution, unbalanced and totally lacking in objectivity".
Meanwhile Ms Dick, gold commander of the Scotland Yard operation on the day, who spent four days giving evidence, said she was outraged at the perceived questioning of her integrity by the prosecution.
She is one of four senior officers still facing possible disciplinary charges over the shooting.