One of four American prisoners released by Iran, Nosratollah Khosravi-Roodsari, was not on the Swiss plane that left Tehran on Sunday, a senior U.S. official said.

While it was not immediately clear whether he opted to stay in Iran or depart separately, an earlier State Department statement said “those who wished to depart Iran have left.”

The official said those that boarded the plane from Tehran included Jason Rezaian, the Washington Post’s Tehran bureau chief, Saeed Abedini, a pastor from Idaho, and Amir Hekmati, a former Marine from Flint, Michigan.

Rezaian’s wife and mother are also both on the plane.