A jury member has said that the photo is 'morally as problematic to publish as a terrorist beheading.'
Turkish photographer Burhan Ozbilici has won World Press Photo of the Year.
The Associated Press photographer won the honour for his image of off-duty police officer Mevlüt Mert Altıntaş, taken moments after he assassinated Russia’s Ambassador to Turkey at a gallery in the Turkish capital of Ankara.
Ambassador Andrei Karlov can be seen lying on the floor in the background, shot in the back.
The image was taken on December 19 last year.
Jury member Mary Calvert said: “Every time it came on the screen you almost had to move back because it’s such an explosive image.
“It was a very, very difficult decision, but in the end we felt that the picture of the year was an explosive image that really spoke to the hatred of our times.”
Jury member João Silva said it was an image which captured his feeling that the world was marching towards the edge of an abyss.
“This is a man who has clearly reached a breaking point and his statement is to assassinate someone who he really blames, a country that he blames, for what is going on elsewhere in the region,” he said.
“I feel that what is happening in Europe, what is happening in America, what is happening in the Far East, Middle East, Syria, and this image to me talks of it. It is the face of hatred.”
But the image has proven controversial for some.
Jury member Stuart Franklin slammed the decision in an opinion piece for The Guardian.
“An image depicting a premeditated murder, staged at a press conference to maximise publicity, is World Press Photo of the Year,” he wrote.
“Placing the photograph on this high pedestal is an invitation to those contemplating such staged spectaculars: it reaffirms the compact between martyrdom and publicity.”
Franklin said that while the photo was impactful, he was strongly opposed to it becoming photo of the year.
“I narrowly lost the argument. I voted against,” he wrote.
“It’s a photograph of a murder, the killer and the slain, both seen in the same picture, and morally as problematic to publish as a terrorist beheading.”
Other jurors have emphasised they were rewarding the photographer, not the crime.
Mr Ozbilici told the World Press Photo Foundation that he wasn’t even officially assigned to cover the event, but learnt of it from a friend.
“I didn’t know the Russian ambassador was going to be there. I didn’t even know the exhibition was about Russia,” he said.
The photographer arrived 15 minutes late and began taking photos.
“Then, suddenly I heard a gunshot. It was very loud. People were running away in panic, and the ambassador’s body was lying on the ground.”
The photographer said he was scared, but focused on the movements on the gunman, trying to analyse whether he would shoot others in the gallery.
“I remember thinking, I might be killed or injured, but the Russian ambassador has been shot. This is very big news, so as a journalist it is my responsibility to stand and do my work,” he said.
"Even if I was killed, there would still be photos."