Iran has freed an American graduate student imprisoned for three years in Tehran amid a prisoner swap. Princeton graduate student Xiyue Wang was conducting research in Iran when he was arrested in August 2016 and sentenced to 10 years in prison on espionage charges that U.S. officials called groundless. In exchange, the United States has freed Iranian scientist Masoud Soleimani, who was arrested at a Chicago airport last year and was convicted on charges of violating U.S. sanctions against Iran.