On his way home, AP photographer Burhan Ozbilici stopped at the opening of a photo exhibit at Ankara’s Contemporary Arts Center. The Russian ambassador to Turkey was to speak, and Ozbilici figured the AP could use images of the envoy for its archives.

Shockingly, Ozbilici instead found himself a witness to an assassination. With cool head and steady hands, he documented the killing of Ambassador Andrei Karlov, capturing some of the most astonishing images of this or any other year. His photo of the raging gunman _ one hand holding the gun, the other pointed to the ceiling, his lifeless victim on the floor _ would appear on countless front pages and broadcasts and websites. Within hours, it was seen by some 18 million people on Facebook alone.

Even in a year of remarkable work by AP staffers, Ozbilici’s photos and actions were extraordinary _ and richly deserving of the final Beat of the Week award of 2016.

At first, Ozbilici would recount in a first-person story, he thought he was witnessing some sort of “theatrical flourish” when the man in a dark suit and tie pulled out a gun. But then there were at least eight shots, and the crowd screamed and scrambled for safety. “I was afraid and confused,” he wrote, “but found partial cover behind a wall and did my job: taking photographs.”

He photographed the shooter as he wandered the room, pointing his gun. He photographed onlookers huddling on the floor in fear.

"I’m here. Even if I get hit and injured, or killed, I’m a journalist. I have to do my work."

“I was, of course, fearful and knew of the danger if the gunman turned toward me,” he wrote. “But I advanced a little and photographed the man as he hectored his desperate, captive audience.

“This is what I was thinking: `I’m here. Even if I get hit and injured, or killed, I’m a journalist. I have to do my work.’

“I could run away without making any photos,” he thought. “But I wouldn’t have a proper answer if people later ask me: `Why didn’t you take pictures?’” He recalled “friends and colleagues who have died while taking photographs in conflict zones over the years.”

He snapped his shutter until security guards ordered the hall vacated, and he left. It was only after he returned to the office to edit his photos that he realized that he had caught the assassin, identified by Turkish authorities as an off-duty police officer, standing calmly behind Karlov before the shooting.

Despite the chaos of the moment, Ozbilici’s photos are composed, documentary storytelling at its finest. And they were not the extent of his contribution to the AP’s coverage that day. He called Ankara writer Suzan Fraser and told her what he had seen, allowing AP to report of the attack quickly in text. Once outside the building, he also took 20 seconds of video on his phone, showing emergency vehicles. After his images were filed, he headed back to the scene, where a video freelancer interviewed Burhan about what he had witnessed. And he offered his first-person account for text.

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Andrei Karlov, the Russian Ambassador to Turkey, pauses during a speech at a photo exhibition in Ankara on Monday, Dec. 19, 2016, moments before a gunman opened fire on him.

AP Photo / Burhan Ozbilici

The accolades came almost immediately.

"I can't imagine how traumatic it was for those who were there at the time," wrote Serbian writer/photographer Dunja Djudjic, on the website DIY Photograph. "But thanks to a brave and extremely professional photographer, we are left with some of the most powerful and shocking documentary photos of this year."

“What bravery AP's @BurhanOzbilici showed to capture those photos,” tweeted Barry Malone, an editor for Al Jazeera. “Wire staff very often unsung and very often the heroes of this trade.”

“A stunning display of courage in the interest of journalism,” wrote blogger Bob Collins of Minnesota Public Radio.

And one of more than 7,000 comments left on AP Images: "Tragic story but this is one of the greatest news photos I've ever seen."

For his artistry under fire and heroic dedication to news, Burhan Ozbilici wins this week’s $500 prize.