London attack caps week of terror fears in Europe.

On Wednesday, a 52-year-old British man, Khalid Masood, killed four people — including an American tourist from Utah — when he rammed a rental car onto the sidewalk of Westminster Bridge, then stabbed an unarmed police officer in an 82-second blitz called the deadliest terror attack to hit the United Kingdom in 12 years. Masood was shot dead by police after he tried to run into Parliament armed with a knife. The Islamic State initially accepted responsibility for the attack, but authorities believe Masood was merely inspired by ISIS. Masood had been linked previously to violent extremism. Investigators are still assessing whether the attacker plotted alone or acted as part of a broader conspiracy. Last Saturday, an attacker was shot at Paris’ Orly Airport after wresting a rifle from a female soldier. He allegedly said, “I’m here to die in the name of Allah. Whatever happens, people are going to die.” On Thursday, Belgian authorities thwarted a suspected terrorist attack after a Frenchman drove his car at high speed through a busy shopping area. No one was injured.

Matt Dunham / Associated Press A woman holds up a sign at a vigil Thursday at Trafalgar Square for the victims of Wednesday’s attack in London. The suspect, who was fatally shot, reportedly had visited Saudi Arabia several times between 2005 and 2009.