A Princeton University graduate student held in an Iranian prison for more than three years was released after a prisoner swap Saturday. 

Xiyue Wang is a Chinese-born naturalized American citizen and doctoral student of history at Princeton. He was arrested and convicted of espionage in 2016 while doing research in Iran for his Ph.D.

Rep. Chris Smith says Wang had all the proper clearances to travel and he was detained in Tehran unjustly.

The swap took place in Surich, Switzerland. It involved Wang and Iranian scientist Massoud Soleimani, who was imprisoned in the U.S. for violating sanctions.

Click here to watch News12 New Jersey's segment on a May 2018 rally for Xiyue Wang.

Sen. Cory Booker says this was a big win for the state and the country. He says, "This is the outcome that New Jerseyans and those around the globe who followed this unjust and politically motivated ordeal had hoped for…I'm grateful for the efforts of those who worked tirelessly and quietly behind the scenes to help bring Xiyue Wang home."

In a statement, Princeton University President Chris Eisgruber writes, "The entire Princeton University community is overjoyed that Xiyue Wang can finally return home to his wife and young son, and we look forward to welcoming him back to campus...We are grateful to everyone, at Princeton and beyond, who has supported Xiyue and his family throughout his unjust imprisonment, and for all the efforts that have led to his release.” 

Wang's wife, Hua Qu, released a statement saying, “Our family is complete once again.” Wang's son was 3 years old when he went to Iran.

President Donald Trump thanked Iran for the fair negotiation. Wang was flown to Germany to be evaluated by doctors. Western detainees from the U.S. and elsewhere remain held by Tehran.

AP Wire Services were used in this report.