NORFOLK, Va. (AP) — The shooter who opened fire in a classroom at Virginia’s Old Dominion University on Thursday in an attack being investigated as an act of terrorism had a gun with an obliterated serial number, potentially complicating investigators’ efforts to determine how the man with a previous felony conviction obtained a firearm, according to a law enforcement official. Investigators will have to try to re-surface the number in order to trace the gun, according to the official, who