A man is treated by emergency services, as a knife lays on the floor, outside the Houses of Parliament London, Wednesday, March 22, 2017. (Stefan Rousseau/PA via AP)
Mark Rowley, Assistant Commissioner for Specialist Operations in the Metropolitan Police, speaks to the media outside Scotland Yard in London, Wednesday, March 22, 2017. (Victoria Jones/ PA via AP)
Police forensic officers at the scene close to the Houses of Parliament in London, Wednesday, March 22, 2017. (Yui Mok/PA via AP)
Emergency services on Westminister Bridge after a policeman was stabbed and his apparent attacker shot by officers. (Dominic Lipinski/PA via AP)
Emergency services staff provide medical attention close to the Houses of Parliament in London, Wednesday, March 22, 2017. (Matt Dunham/AP)
Armed police walk past emergency services attending to injured people on the floor outside the Houses of Parliament, London, Wednesday, March 22, 2017. (Stefan Rousseau/PA via AP)
Armed police outside the the Houses of Parliament, London, Wednesday, March 22, 2017. (Stefan Rousseau/PA via AP)
An injured man sits covered with a blanket as emergency services staff provide medical attention to injured people on the south side of Westminster Bridge. (Matt Dunham/AP)
Conservative MP Tobias Ellwood, left, stands amongst the emergency services at the scene outside the Palace of Westminster, London, Wednesday, March 22, 2017. (Stefan Rousseau/PA via AP)
"Foreign office minister Tobias Ellwood looking like he's sporting fresh blood." (Hugh Dickinson/Twitter)
"Parliament staff have been escorted to Westminster Abbey. Everyone's details will be taken." (Tim Kaplan/Twitter)
Parliament member Barry Sheerman posted this photo from inside the lock-down. (Barry Sheerman/Twitter)
People inside Parliament were being escorted out, wrote Twitter user Tim Kaplan when posting this photo. (Tim Kaplan/Twitter)
Parliament member Barry Sheerman shared this photo showing Parliament members waiting while in lockdown. (barry Sheerman/Twitter)
Emergency services staff provide medical attention close to the Houses of Parliament in London, Wednesday, March 22, 2017. (Matt Dunham/AP Photo)
Armed police officers gather outside of the Houses of Parliament in London, Wednesday, March 23, 2017. (Kirsty Wigglesworth/AP Photo)
Armed police officers enter the Houses of Parliament in London, Wednesday, March 23, 2017. (Kirsty Wigglesworth/AP Photo)
Emergency services staff provide medical attention close to the Houses of Parliament in London, Wednesday, March 22, 2017. (Matt Dunham/AP Photo)
Police secure the area close to the Houses of Parliament in London, Wednesday, March 22, 201. (Matt Dunham/AP Photo)
Emergency services staff provide medical attention close to the Houses of Parliament in London, Wednesday, March 22, 2017 (Matt Dunham/AP Photo)
Police secure the area close to the Houses of Parliament in London, Wednesday, March 22 following reports of violence. (Matt Dunham/AP Photo)
Police secure the area close to the Houses of Parliament in London, Wednesday, March 22 following reports of violence. (Matt Dunham/AP Photo)
Police secure the area close to the Houses of Parliament in London, Wednesday, March 22 following reports of violence. (Matt Dunham/AP Photo)
Armed police officers enter the Houses of Parliament in London, Wednesday, March 23, 2017 after the (Kirsty Wigglesworth/AP Photo)
Armed police officers enter the Houses of Parliament in London, Wednesday, March 23 after the House of Commons sitting was suspended as witnesses reported sounds like gunfire. (Kirsty Wigglesworth/AP Photo)
An armed police officer stands on Parliament Square outside of the Houses of Parliament in London, Wednesday, March 23 after witnesses reported sounds like gunfire outside. (Kirsty Wigglesworth/AP Photo)
Police secure the area on the south side of Westminster Bridge close to the Houses of Parliament in London, Wednesday, March 22, 2017. (Matt Dunham/AP Photo)