Police say the driver is under arrest after plowing into the crowd at a Christmas market in Magdeburg, Germany, killing at least five people - including a 9-year-old - and injuring 200 others.

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.