The senior policewoman who led the operation that ended in Jean Charles de Menezes's death choked back tears as she revealed she thinks about what happened every day.
Deputy Assistant Commissioner Cressida Dick told an inquest she felt "terrible" when she learnt the innocent Brazilian had been shot dead by police marksmen after being mistaken for a terrorist.
She described Mr de Menezes's death as "an awful tragedy" - but insisted the officers under her command did nothing wrong that day.
The victim's mother, Maria Otone de Menezes, was said to be "disappointed and offended" by the senior policewoman's comments.
Mrs de Menezes, 63, attending the inquest for the first time, broke down and had to leave the courtroom as Ms Dick recounted the events that led to her son's death.
Mr de Menezes, 27, was shot seven times in the head at Stockwell Tube station in south London on July 22 2005 after being mistaken for failed suicide bomber Hussain Osman.
Ms Dick was in charge of the Scotland Yard control room overseeing the pursuit of the Brazilian by surveillance and firearms officers who feared he was the on-the-run terrorist.
Nicholas Hilliard QC, counsel to the inquest, asked the senior officer how she felt when she learnt that an innocent man had been shot.
Ms Dick replied: "Terrible. It was a terrible thing to happen. And from that day to this I have thought about this often, every day - wondered what we could have done differently, if anything, did we act reasonably? I set out that morning to protect the people of London and to save people, and the last thing I wanted to do is have an innocent person shot. But that is what happened and I regret it deeply."
The inquest at the Oval cricket ground, now in its third week, was adjourned.
