Iran Prisoner Swap: Inside the Frantic Final Moments

New details are emerging about the tense moments before the American left Iran.

Kerry quickly made another call to Iranian Foreign Minister Javad Zarif to settle the issue. Kerry told Zarif that Salehi's passage had always been part of the agreement. "Then it took a while," this official said, leaving them to wondering nervously if she would make it on the plane. Eventually she was allowed on and the plane got underway early in the morning eastern time, more than 12 hours after news of their release had broke.

US Special Envoy in the war against ISIS, Brett McGurk, met Jason and the other Americans at the airport in Geneva when the plane landed.

Salehi, along with Jason's mother Mary Rezaian, had been tireless advocates for his release.

Get real-time updates as this story unfolds. To start, just "star" this story in ABC News' phone app. Download ABC News for iPhone here or ABC News for Android here.