The suspect in the attack in Germany had history of threats and harassment though no record of violence and an ideology that didn’t fit familiar patterns.

The latest deadly assault on a beloved German tradition illustrates the challenge of holiday safety. For years, Germany has been strengthening security measures around Christmas markets in reaction to an attack in 2016 in which a man killed 12 people by driving a truck into a market in central Berlin.

Abdulmohsen, a 50-year-old doctor from Saudi Arabia, had expressed anti-Islamic views and described himself as a Saudi dissident, an official said.