A U.S. law enforcement official identified the suspect as Ryan Wesley Routh, 58, of Hawaii. The official spoke on the condition of anonymity because the investigation is continuing. Mr. Routh was interviewed by The New York Times in 2023 for an article about Americans volunteering to aid the war effort in Ukraine. Mr. Routh, who had no military experience, said he had traveled there after Russia’s invasion in 2022 to recruit Afghan soldiers for the fight. He told The Times he once visited Washington to meet with politicians to strengthen support for Ukraine. “I’m just a U.S. citizen that’s helping out,” he said.