Over the space of a few hours on Monday, an assassin in Ankara gunned down the Russian ambassador to Turkey; a truck plowed through a Christmas market in Berlin, killing 12 people; and a gunman opened fire at a Muslim prayer center in Zurich, wounding at least three people.

Here’s what is known about each attack.

Ankara, Turkey

• The Russian ambassador to Turkey, Andrey G. Karlov, was shot and killed at an art exhibition in the Turkish capital, in front of horrified onlookers. The attack was captured on video.

• The gunman shouted in Arabic “God is great!” and added, in Turkish, “Don’t forget Aleppo, don’t forget Syria!” Police officers shot and killed him. He was later identified as Mevlut Mert Altintas, 22, a graduate of a police college in Izmir.

• Russian investigators have arrived in Turkey; the plane that carried them will take Mr. Karlov’s body back to Russia.