A car is seen crashed into a fence outside the Parliament building in London on Wednesday, March 22. Police have launched a "full counter-terrorism investigation" after an attacker rammed a car into crowds of people and stabbed a police officer on Parliament grounds. Courtesy James West

An armed police officer stands over the attacker, identified as Khalid Masood, outside Parliament. "It appeared that a car was coming towards the House of Commons mowing down pedestrians on the way," Member of Parliament Gerald Howarth told CNN. "The driver then got access to the parliamentary estate, stabbed a police officer and was shot." Stefan Rousseau/PA via AP

Masood is treated by emergency services as police look on at the scene outside the Houses of Parliament. The Metropolitan Police say he was born in Kent, but is believed to have been living in the West Midlands recently. Police say Masood was also known by a number of aliases. "Masood was not the subject of any current investigations and there was no prior intelligence about his intent to mount a terrorist attack," Met Police said in a statement. Stefan Rousseau/PA via AP

Member of Parliament Tobias Ellwood, in the glasses, tends to one of the injured people amid the chaos. The man the politician was trying to save was a police officer who died, a witness on the scene told CNN. Authorities identified the deceased officer as Keith Palmer, 48. Stefan Rousseau/PA via AP

Emergency workers attend to injured people at the scene. PA Images/Sipa USA

Medics treat a victim on Westminster Bridge. Rex Shutterstock via ZUMA Press

People leave the Parliament building after the incident. Lawmakers were forced to remain in the main debating chamber of the House of Commons as police responded to the incident outside. DANIEL LEAL-OLIVAS/AFP/Getty Images

A person is treated at the scene. Yui Mok/AP

Medical aid is provided outside Parliament. Matt Dunham/AP

Tourists were trapped for a time in cars on the London Eye Ferris wheel, which was stopped in the immediate aftermath of the attack. James Gourley/Rex Shutterstock via ZUMA Press

A police officer stands guard near Westminster Bridge and the Houses of Parliament. Jack Taylor/Getty Images

A person receives medical treatment at the scene. Carl Court/Getty Images

At right, the car of British Prime Minister Theresa May is driven away from Parliament. DANIEL LEAL-OLIVAS/AFP/Getty Images

An air ambulance arrives at the scene. DANIEL LEAL-OLIVAS/AFP/Getty Images