<sod >ÃÂÃÂ  Police said the attacker, who is believed to have acted alone, then entered the gates of New Palace Yard and repeatedly stabbed a male police officer.< eod>< sod > Police said the attacker, who is believed to have acted alone, mounted the pavement of the bridge and mowed down more than a dozen tourists, local workers and police officers before crashing into the Parliament railings.< eod>