The authorities said they had identified a suspect in Wednesday’s bombing of a passenger bus in the central Russian city of Togliatti that killed eight people and wounded more than 50, mostly local university students. The bomber was likely aboard the bus at the time of the explosion, said Aleksandr Bastrykin, the head of the prosecutor general’s investigative committee. Mr. Bastrykin said a search of the suspect’s apartment had turned up “elements that could have been used to build a homemade explosive device.” He refused to provide the suspect’s name or say if the suspect was killed in the blast.