One of the police marksmen who killed Jean Charles de Menezes told an inquest today he believed he was facing "immeasurable" danger that day.
The officer, from Scotland Yard's elite CO19 specialist firearms unit, said he was aware he could be required to tackle one of the failed 21 July suicide bombers.
The highly-experienced marksman - identified by the code name C12 - has never spoken about the shooting of Mr de Menezes in public before.
On 22 July 2005 C12 and his team were told they would have to detain any suspects who emerged from a block of flats in south London linked to Hussain Osman, one of the terrorists from the day before.
The firearms officer was asked about his state of mind after being briefed on the operation.
His voice quavered as he told the inquest: "The danger we were facing, or potentially facing, would be immeasurable.
"They were failed suicide bombers. Who knows what their mind set would be? They had prepared devices in order to achieve mass murder.
"They were determined, as we were led to believe, prepared, highly dangerous, and we might have to face them."
C12 added: "There was a possibility in my mind - bearing in mind the incidents that had happened the day before - that we may need to face potential failed suicide bombers."
The inquest heard that a senior firearms adviser, identified as Trojan 84, warned C12 and his colleagues they might need to employ "unusual tactics" that had not been used before.
Mr de Menezes was shot seven times in the head at point-blank range inside Stockwell Tube station in south London after being mistaken for failed suicide bomber Osman.
C12 was watched in the courtroom as he gave evidence by the Brazilian's mother, Maria Otone de Menezes, 63, and brother, Giovani da Silva, 36.Reuse content