American Train Attack Witness Hospitalized in Paris

French President Francois Hollande bids farewell to U.S. Airman Spencer Stone, U.S. National Guardsman Alek Skarlatos (second from left), and Anthony Sadler (R), a senior at Sacramento State University in California, after Hollande awarded them the French Legion of Honor at the Elysee Palace, in Paris, on Aug. 24, 2015. Michel Euler/AP Photo

PARIS—An American who had been scheduled to appear as a star witness at the trial in Paris of an ISIS terrorist was hospitalized Thursday in the French capital, casting doubt on whether he would still be able to testify about his role in the dramatic capture of the gunman that averted a possible mass slaughter aboard a high-speed train.

Spencer Stone’s lawyer, Thibault de Montbrial, wouldn’t give details about what is ailing the former U.S. airman, citing medical privacy. He said Stone would not testify as planned on Thursday afternoon.