Northern Syria — In northern Syria, prisoners are filled to the point of bursting, with foreign ISIS fighters. They want to return to their home countries, but nobody wants them. CBS News was given rare access to one of these prisons, the first time a television crew has been allowed in.

It's home to 5,000 ISIS captives, including ISIS leaders and the men who built their deadly bombs, according to the guards. But it's not where CBS News expected to find a 22-year-old man from Minneapolis. Abdelhamid Al-Madioum agreed to tell his story, but we can't know for sure whether he was speaking freely.

He said he was recruited to ISIS through a contact on Twitter and was bombarded with ISIS propaganda videos. Not the ones showing gruesome beheadings, but ones explaining that ISIS was helping Muslims.

He said he entered ISIS territory in 2015, hoping to become a doctor.

"They gave me a blank check to buy whatever I wanted," Al-Madioum said. "Here's the thing. People like me that see this, don't really believe the news."

He thought ISIS terrorism was fake news. Like many in the prison, he claims he was never an ISIS fighter. Instead, he said he was a victim, and said he lost his arm in a U.S. airstrike.

Others at the prison also have terrible injuries and some are children. But there's no question this is a dangerous place.

The guards showed CBS News an attempted prison break from just four days ago. They want foreign governments to take their citizens home so they can't escape and rejoin ISIS insurgents.

Al-Madioum claims he was interrogated by FBI agents, who said he could face 15 years in prison in the U.S.

"Fifteen years is a very long time for mistakes you made coming to Syria," he said, adding that he deserves to be forgiven.

ISIS may have lost control of its so-called Islamic State, but these men have been left behind and it's often impossible to tell who among them is still dangerous.