Beau Solomon, 19, of Spring Green, Wisconsin, was in Rome to study at John Cabot University. He disappeared the night of July 1, police said, after he was last seen in a bar not far from the Tiber River.
John Cabot University confirmed that his body was found in the river Monday morning.
The pope "expressed his deepest sympathy and compassion and his closeness in prayer to the Lord for the young man who died so tragically," according to a statement released by the Rev. Federico Lombardi, the director of the Holy See press office.
Italian police said Tuesday a Roman man, Massimo Galioto, 40, was detained in connection with Solomon's death, suspected of aggravated murder without motive.