(NewsNation) — After Kirillo Alexandrov, an American living in Ukraine, was captured by Russian forces, he says he was subject to beatings, mock executions and nails in his food.

The 37 days Alexandrov spent imprisoned in the closet of an abandoned building were “very rough,” he told Connell McShane on “NewsNation Now” Tuesday.

He finally got out after being rescued by Project Dynamo, a veteran-led organization that evacuates Americans out of conflict zones.

Alexandrov had been held on what he calls “nonsensical” spying and espionage charges. Now, the Department of Justice charged four soldiers who held Alexandrov with torture, inhuman treatment and unlawful confinement of a U.S. national in Ukraine.

“It’s very humbling that the State Department cared to push this through,” Alexandrov said. “Hopefully it changes policy, and it’s very humbling that there are good people like Bryan (Stern, CEO of Project Dynamo) out there to save people, and I wouldn’t be here if it weren’t for him.”

Stern said to this day, the Russians still don’t know how they saved Alexandrov.

“When you think about it, you’re probably thinking grenades and machine guns and everything,” Stern said. “It’s not that at all.”

Russian negotiators who had been working with Project Dynamo called the group after it conducted the rescue, not knowing Alexandrov had been freed.

“We were the ones that told Russia that we had him,” Stern said. “They didn’t even know.”

Added Stern: “No private entity has ever gotten nose-to-nose with the Russian intelligence service this way, and been successful this way, to the extent that we were able to rescue an American and been able to enable the Department of Justice to leverage an indictment for the first time in American history.”