U.S.-born game designer Amir Mizra Hekmati has been released from Iran after being held in custody for over four years.

Hekmati, who was previously sentenced to death after allegedly confessing to spying on the country and creating propaganda games for the C.I.A., was released as part of a prisoner swap that also involved Washington Post correspondent Jason Rezaian, Christian preacher Saeed Abedini, and Nosratollah Khosravi-Roodsari.

According to an NBC report, Hekmati - whose death sentence was overturned in 2012 - left Iran on Sunday, January 17. His plane, which was also carrying Rezaian and Abedini, then landed in Geneva before heading on to Germany. 

U.S. State Department special envoy Brett McGurk confirmed the men had safety left the country on Twitter. 

"It is hard to put into words what our family feels right now. But we remain in hopeful anticipation until Amir is in our arms. As many of you know, Amir’s father is very ill and soon he will embrace his son once more," said the Hekmati family via Facebook.

"We are incredibly grateful for today’s news. We thank our government, and we thank all of you whose thoughts and prayers helped us tremendously since Amir was taken from us in 2011."

A former U.S. Marine, Hekmati worked at Kuma Reality Games, the studio behind the KumaWar first-person shooter series. KumaWar featured episodes in which players killed militant Islamist figures, and led a U.S. assault on Iran in order to cripple its nuclear weapons program.

The New York City-based developer had previously accepted contract work from the U.S. government to develop training software for military applications, including "Second Language Training," a language retention training program commissioned by the Department of Defense.

While in detention Hekmati purportedly made a number of public confessions incriminating himself and Kuma, however, according to the White House, the Iranian-American game designer was simply in Iran visiting his grandmother.

In an attempt to clarify the situation and shed light on Kuma's motivations, Polygon made a public records request of the C.I.A. in October last year. That request that was subsequently denied.