Scotland Yard has denied that a close aide of chief Sir Ian Blair knew an innocent man had been shot dead on the London Tube six hours after the death.
Sir Ian could face new questions over the claim
The Met Police said the claim, learnt of by the BBC, was "simply not true".
Sir Ian has always said he did not know the victim was innocent Brazilian Jean Charles de Menezes until the next day.
Mr Menezes was shot dead at Stockwell station after being mistaken for a terrorist suspect, the day after the 21 July alleged bombing attempts.
The 27-year-old was shot seven times in the head by armed officers from the Metropolitan Police.
Sir Ian maintained that he did not know the wrong man had been shot for 24 hours. On the day of the shooting, Sir Ian said it was "directly linked to the ongoing and expanding anti-terrorist operation".
A claim has emerged that a member of Sir Ian's private office team believed police had targeted the wrong man six hours after the shooting.
BBC home affairs correspondent Margaret Gilmore said independent investigators examining the matter were told this by a senior officer.
But a Met spokesman said the officer "alleged to have had the information... has categorically denied this in his interview with, and statement to, the IPCC investigators".
"This has also been corroborated by other staff in the private office," the spokesman added.
"We are satisfied that whatever the reasons for this suggestion being made, it is simply not true."
An IPCC spokesman called any speculation "unhelpful".
"We'll be doing a fair and impartial investigation," he added.
"We have not reached any conclusions yet. We suggest others wait for our investigation and not jump to conclusions prematurely.
"We will be making our decision on facts and not speculation."
Mr Menezes was shot after police mistook him for a suicide bomber
As part of its inquiry into the shooting, the IPCC has sent a report to the home secretary, the Inner South London Coroner John Sampson, and Her Majesty's Chief Inspector of Constabulary, Sir Ronnie Flanagan.
The report has also been sent to Scotland Yard, the Crown Prosecution Service (CPS) and Metropolitan Police Authority to enable them to make any changes to operational procedures without having to wait for the IPCC's findings to be made public.
The report's contents are not being disclosed while the CPS is considering whether to bring criminal charges against the police involved in the shooting.
The publication could be years away as any criminal matters have to be resolved first and an inquest into Mr Menezes' death still has to be held.
The CPS says it hopes to decide by Easter whether any officers will face criminal charges.
Sir Ian is already being investigated over whether police misled the public in any way after the shooting.
He is also under pressure after having to apologise this week for taping a phone call with the attorney general and taping senior officials from the Independent Police Complaints Commission without their consent.