A Turkish police officer who was standing behind Russia's ambassador to Turkey, Andrey Karlov, as he gave a speech at an art gallery in the Turkish capital.
Moment later, he drew a handgun and shot Mr Karlov nine times before reportedly shouting "Allahu Akbar."
He is understood to have added, in a mixture of Turkish Arabic, words to the effect of: "We made an oath to die in martyrdom...it is revenge for Syria and Aleppo...until they are safe, you will not taste safety."
Russia's foreign ministry has described his actions as a "terrorist attack."
What do we know about him?
Melih Gokcek, the mayor of Ankara, has confirmed that the gunman worked in the city as a police officer, but little else is known about him at this early stage.
Turkish media reports say he was 22 years old, and one local newspaper described him as an "agile" police officer who worked on special operations.
Turkish authorities confirmed that he had been serving in Ankara's riot police unit for the last two-and-a-half years.
He was clean-shaven and wore a black suit with a matching belt and tie.
Seconds before the attack he was captured on camera by an AP photographer standing innocuously behind Mr Karlov as he gave a speech.
According to CNN, the words spoken by the attacker are similar to the unofficial anthem of the al-Qaeda-allied group Al Nusra.
A picture of the gunman wearing his police uniform has been widely circulated by the Turkish media, which identifies him as M. Mert Altintas.
Police officers standing outside the gallery said they believed the gunman was off-duty when the attack took place.
Turkish media reports said the gunman attended Korfez Preparatory School.
Turkish news agency Anadolu, without citing sources, said the shooter's family home in the western province of Aydin was searched and his mother, father and sister were detained.
Anadolu also says the man's house in Ankara was raided and his roommate, also a riot police officer, was detained.