Detective Chief Inspector Harry Hennigan has defended the decision by authorities to let a man out on day release from prison, who subsequently carried out a series of armed raids.
Sean Bradish was handed down two life sentences having already received one previously.
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PC Keith Palmer, 48, stabbed by Khalid Masood while on duty in the grounds of the Palace of Westminster last Wednesday.
Those gathered on the bridge fell silent at 2.40pm - the time the first call was made to police exactly seven days ago.
Simon Lucy, 61, filmed hundreds of hours worth of footage on the London Underground network.