The Westminster terror attack lasted only 82 seconds, Scotland Yard has said.
Khalid Masood's attack began at 2.40pm on Wednesday, and was over by 2.42pm, according to a detailed investigation by the Metropolitan Police's Counter Terrorism Command.
The car the terrorist was driving first mounted the northbound pavement on Westminster Bridge at 2.40pm and eight seconds.
Police say he then continued towards Bridge Street along both the footpath and road, before crashing into the Palace of Westminster's perimeter fence at 2.40pm and 38 seconds.
The first 999 call to the Met was made at 2.40pm and 59 seconds.
Masood then left his car and was "shot by a police firearms officer inside the Palace of Westminster boundary" at 2.41pm and 30 seconds.
Deputy Assistant Commissioner Neil Basu, senior national coordinator for UK Counter Terrorism Policing, said: "We still believe that Masood acted alone on the day and there is no information or intelligence to suggest there are further attacks planned."
But while he added that police "need to establish with absolute clarity why he did these unspeakable acts", DAC Basu acknowledged "there is a possibility we will never understand why he did this".
"That understanding may have died with him," he added.
He continued: "Nevertheless, we are determined to understand if Masood was a lone actor inspired by terrorist propaganda or if others have encouraged, supported or directed him.
"If the latter proves to be the case, they will face justice.
"Whilst the attack lasted only 82 seconds it will remain in the memories of many forever.
"The thoughts of all those working on this investigation are with those so deeply affected."
:: Anyone who has information to contribute about the attack is asked to call the anti-terrorist hotline on 0800 789 321.