Russian authorities announced Tuesday that a suicide bomber is believed to have been behind the Monday blast on the St. Petersburg subway that left 14 dead. Officials said they believed a native of Kyrgyzstan who became a Russian citizen was involved in the attack, but declined to name him. However, Kyrgyzstan’s national-security agency identified him as Akbarzhon Dzhalilov, a 22-year-old born in the city of Osh. No one has claimed responsibility for the bombing. Investigators worked Tuesday to piece together what led up to the explosion, and said parts of a suspected bomber were found amid the rubble in the underground system. Forty-nine people remain hospitalized. Russian President Vladimir Putin was in St. Petersburg, his hometown, when the bomb went off, and law-enforcement officials say they are attempting to determine if his visit was among the suspect’s motives. U.S. President Donald Trump reportedly phoned Putin on Monday to offer America’s “full support” in the matter.