BLACKSBURG, Va. -- The man who authorities say killed a Virginia Tech police officer was described as a typical college student in many ways, making it difficult to understand why he would commit an armed robbery and then, apparently at random, target the patrolman before killing himself. The gunman was identified Friday as Ross Truett Ashley, a 22-year-old part-time business student at Radford University, about 10 miles from the Virginia Tech campus in Blacksburg. He first drew authorities'attention Wednesday when, they say, he walked into his landlord's office with a handgun and demanded the keys to a Mercedes-Benz SUV.