Last week’s terrorist attack in London, which left four people dead, wounded dozens more and led to the temporary lockdown of Parliament, was a grim reminder of the daily threat Europe faces from extremist violence.
It also showed the challenges for intelligence and security services in confronting individuals who, like the 52-year-old attacker, British-born Khalid Masood, are intent on causing mayhem and destruction armed with low-tech weapons, such as sports utility vehicles and kitchen knives.
British authorities are still trying to understand how the attacker, who was not considered a serious terrorist threat by British security