An American held behind enemy lines accused of war crimes and espionage has been rescued after being detained by Russian forces for over a month while trying to escape Ukraine

Project Dynamo co-founder Bryan Stern, who helped facilitate Kirillo Alexandrov's safe return, explained why it was the most difficult rescue to date Thursday on "Fox & Friends First."

"We've done all kinds of things that were hard and complex through our existence," Stern told co-host Carley Shimkus. "But this is our first… charged American citizen victim of war crimes, falsely accused of espionage in captivity, rescue that we've ever done."

Project Dynamo, Detroit Lions Rescue Mission of Kirillo Alexandrov May 11, 2022 with co-founder Bryan Stern.

Project Dynamo, Detroit Lions Rescue Mission of Kirillo Alexandrov May 11, 2022 with co-founder Bryan Stern. (Project Dynamo)

"So when you try and say all that, it's a mouthful by itself," he continued. "That just leads to the complexity of the operation, which… this was a win, but it was a hard-fought win. Nothing about this was easy at all."

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Alexandrov, a Michigan native, was captured by Russian forces when he tried to flee his home with his family near Kherson, Ukraine. He was in Russian custody for almost 40 days before he was reunited with his family in Poland on Wednesday. 

Project Dynamo, Detroit Lions Rescue Mission of Kirillo Alexandrov May 11, 2022.

Project Dynamo, Detroit Lions Rescue Mission of Kirillo Alexandrov May 11, 2022. (Project Dynamo)

"When it was at its lowest it was disgusting," Alexandrov said. "I was faced with violence, a mock execution. My wife was faced with violence, and every day was a threat to my family, to my village."

"It was just terrifying," he continued. "The uncertainty was awful."

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Stern said American negotiators had two lines of effort going to secure his release. One was a "unilateral rescue" and the other was negotiations with Russian officials. 

"They were angry and surprised," Stern said. "We had two parallel lines of effort going at the same time. One was negotiation to secure a release and the other was a unilateral rescue. We ultimately did the unilateral action."

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"They actually called us about five hours after we already had him to continue negotiations," he continued. "They didn't even know."

Project Dynamo, a Florida-based veterans group, has helped facilitate the evacuation of hundreds of people from Ukraine.