Andrey Karlov, the Russian ambassador to Turkey, speaks at the opening ceremony of a photo exhibit in Ankara, Turkey, on Monday, December 19. Moments later, he was fatally shot. Associated Press photographer Burhan Ozbilici was at the event and watched the assassination unfold. Burhan Ozbilici/AP

The man holds his gun up after shooting Karlov. The attack occurred at the Cagdas Sanat Merkezi modern arts center in Ankara. Turkish Interior Minister Suleyman Soylu said in a news conference that the gunman was Mevlut Mert Altintas, a Turkish police officer. Burhan Ozbilici/AP

Karlov's body lies on the floor as the gunman stands nearby. STRINGER/AFP/Getty Images

The gunman gestures near the body of Karlov. In a video circulating on social media, the shooter is heard shouting, "Allahu akbar (God is greatest). Do not forget Aleppo! Do not forget Syria! Do not forget Aleppo! Do not forget Syria!" Russia has been instrumental in helping Syrian President Bashar al-Assad's regime in its push to retake the eastern sector of Aleppo, which had been held by rebels for nearly four years. Russia is also the most powerful ally of Assad's regime and has carried out airstrikes since September 2015 to prop up the embattled leader. Burhan Ozbilici/AP

People cower after Karlov was shot. "Get back! Get back!" the gunman could be heard shouting in Turkish.

Burhan Ozbilici/AP

The gunman stands near the body of Karlov. "Only death will remove me from here. Everyone who has taken part in this oppression will one by one pay for it," he said in the video. Burhan Ozbilici/AP