Mstyslav Chernov, a video journalist with the Associated Press, was in the Ukrainian city of Mariupol in February 2022 when Russian troops invaded. When other journalists left, he and his team stayed — and kept filming.

"By the time the city was completely surrounded," the Ukrainian filmmaker says. "I just understood that we need to record everything. Every frame, every second will be invaluable later, for the war crimes investigations, for the history of Ukraine."

Chernov and his team would later win a Pulitzer Prize for their work in Mariupol. The new PBS FRONTLINE and Associated Press documentary, 20 Days in Mariupol, is based on the footage the team captured during the first days of the war in Ukraine. Chernov says he wanted to show audiences what it was like to be trapped in a city that was sliding into chaos.

"You constantly hear and feel and smell the pain," Chernov says. "And the hunger that comes with the siege, people gathering water, people gathering snow outside and running in their shelters just to melt the snow into the water. People scrambling for food in looted shops."

Chernov did his best to capture everything — he documented a bombed maternity hospital and mass graves — but he acknowledges he occasionally had to stop recording because the moments were too hard or the people he was filming needed help. He says war is surprising in the ways that it shows what people are capable of.

"I've seen people who thought they're so brave and they're capable of everything, but then when they're presented with a difficult choice, whether to risk their lives or do something ... they would choose to run," he says. "And those people who I would never expected to be brave and to be standing their ground until the very end, they do it – and it even surprises them."

One doctor Chernov met in Mariupol told him that war reveals qualities in people's character that wouldn't be apparent otherwise: Good people become better. Bad people become worse. "I'm sure there's a better way to understand our own nature. But that's the reality of life in the war zone," Chernov says.

20 Days in Mariupol premieres on PBS FRONTLINE on Nov. 21 and will stream on YouTube, FRONTLINE's website, in the PBS app and on the PBS Documentaries Prime Video Channel.

Interview highlights

On how the team knew to cover Mariupol

For most of Ukrainians and for many journalists who've been covering Ukraine since 2014, this war, this Russian invasion has started in 2014. For me as a conflict journalist, my work has started from there — and for many Ukrainian journalists, too. We just became conflict journalists — cameramen, photographers, writers — we all became war journalists. And that was our new reality. And for all these years of covering other conflicts for Associated Press, ... I was always coming back to Ukraine and to the frontlines and kept trying to bring attention to [the] ongoing conflict. And we knew that Mariupol is significant, symbolic in tactical importance for Russia because it's just on the way to Crimea. And we didn't know what was going to be the scale of the invasion. But in any case, Mariupol would be the big target for them. That's why we have decided to go there.

On witnessing the destruction and suffering in Mariupol

It's very, very personal for all of us. I grew up in Kharkiv, and Kharkiv is a similar city culturally and visually even similar to Mariupol. So being there and seeing the city indiscriminately destroyed and women and children and men, everyone being killed and their homes being destroyed, was just psychologically devastating. And it was definitely the most dangerous experience I've had throughout these years of different wars. But it was crucial at that point that we focused on the human toll, on the effect that these attacks, this invasion, is having on the civilians. Because Russia kept claiming that they're not targeting civilians, that they're targeting only military objects, which was clearly not the case. ... We did expect that they [would] be shooting in the city, but honestly, we did not expect it to be so brutal. No one did.

On being the only team sending images from Mariupol

I was seeing that nothing else [was] being published from Mariupol. ... Editors also were telling us that apparently there is no one else reporting. Now we know that a great Lithuanian filmmaker was in Mariupol at the same time with us filming. He wasn't sending anything and he tried to escape. His name is Mantas Kvedaravicius, and he was trying to escape the same way we did, but slightly later through Russian checkpoints. And unfortunately, he was captured and executed. ...

I have to tell the truth. I am really afraid of death and of pain. But then again, we are not presented with much choice right now. And since I have chosen this profession, I have chosen to challenge myself and my fears. Then I will stick to that decision for as long as I can.

On the moments that are hard to capture on film

A lot of that chaos is in the film, but there are still a lot of moments which are just impossible to capture because visually nothing happens. When you just lie down on the floor of the hospital at night and bombs are falling around the hospital, and when all the patients that are in these corridors — because people wouldn't sleep in wards, they would just sleep on the floor of the corridors of the hospital — all people in pain because there were just very, very little painkillers left and they would suffer and they would moan and they would whisper to each other and they would call for nurses. But then there was just one nurse [who] couldn't even sleep, and she couldn't ease these people's pain. ...

But at the same time, there would be someone with a guitar and he or she would just sit and play and sing. And suddenly everything is transformed and people gather and there's again, full of hope and full of life. So there is this always an emotional rollercoaster of hope and desperation, of chaos and silence. And it goes up and down and it just never stops. And you want it to stop and you desperately want it to stop, but it just doesn't.

On witnessing children dying

You can't prepare yourself for that. And I don't think any normal human being can prepare [themselves] for that. ... But you know that at the moment your feelings are absolutely irrelevant because that's parents who are hit the hardest. I can only imagine how that feels. And I wish that no one ever feels that. I think it is the biggest tragedy in the world, a loss of a child's life. And no one should experience that ever.

On how they escaped Mariupol alive

It was day 20 and the green corridor was just negotiated and opened, although it was not clear whether it's going to hold or not, whether it's official or not, whether people who are leaving through this green corridor will be shot at or not. But thousands of cars were leaving the city and ... we knew that this was our chance. ... We were so lucky to get through 15 Russian checkpoints, like 100 kilometers within the occupied territory. ... We reached a Red Cross convoy. ... And we just went in this convoy. And that saved us, too, through the hardest part of the trip.

Lauren Krenzel and Seth Kelley produced and edited this interview for broadcast. Bridget Bentz, Molly Seavy-Nesper and Beth Novey adapted it for the web.