Firefighters look at a toppled Christmas tree after a truck ran into a crowded Christmas market and killed several people in Berlin, Germany, on Monday, Dec. 19, 2016. Mevlut Mert Altintas, an off-duty police officer, shouts after shooting Andrei Karlov, right, the Russian ambassador to Turkey, at an art gallery in Ankara, Turkey, on Monday, Dec. 19, 2016.