The man with the Syrian passport — which Greek officials said had been registered at the Aegean island of Leros on Oct. 3 — was 25, and died at the stadium. Another assailant, who died at the concert hall, was 29 and a native of Courcouronnes, about 20 miles south of Paris. He had a criminal record and was known to be involved in extremist Islamic ideology, Mr. Molins said. Officials later identified him as Ismaël Omar Mostefaï and said they had detained several of his relatives for questioning.