A police marksman who shot dead Jean Charles de Menezes "embellished" and "grossly exaggerated" his account of what happened on the Tube train because he realised that he had killed an innocent man, an inquest heard today.

The officer, known as Charlie 12, claims he shouted "armed police" before he shot Mr de Menezes at close range even though Tube passengers did not to hear the warning.

He was "so consumed" with what had happened the day before on July 21 2005, when four suicide bombers had failed to detonate bombs on the London transport system, that the only thought in his mind as he chased Mr de Menezes was to deliver a critical shot to his head, it was claimed.

Michael Mansfield, QC, for the family, said that the officer, a member of Scotland Yard’s elite CO19 specialist firearms unit, never really properly assessed the situation.

Anti-terror police were trying to find the failed suicide bombers and Mr de Menezes, 27, who was shot seven times in the head at point-blank range, was mistaken for one of the would-be suicide bombers, Hussain Osman.

Mr Mansfield put it that as soon as the officer believed that as he was dealing with a failed suicide bomber his mind had been made up as to what he was going to do.

"Once you knew he was identified as a potential mass killer from the day before, that was it - do you follow? You are down the escalators and in the carriage and he is dead."

The officer replied that all he wanted to do was to get to the suspect. "I did not have any preconceived ideas about what I was going to do. I didn't even know where he was at that stage, let alone a delivery of a critical shot. I just didn't have that in my mind, I just wanted to know where he was and wanted to find him."

Mr Mansfield said: "I'm going to make it plain that what you did when it came to making a statement the following day was to grossly exaggerate what you saw in order to, as it were, convince people that he had been a terrorist about to explode a bomb in your mind. Is there any possibility you did that?"

Charlie 12 answered: "Absolutely none whatsoever, no."

Mr Mansfield: "I suggest you went straight to the delivery of a critical shot which you have been trained to do."

Charlie 12:"That just didn't happen sir, that just didn't happen."

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