This seems to answer several questions; some of which were asked with in this thread:
WASHINGTON (Reuters) - Seung-Hui Cho took just nine minutes to fire more than 170 rounds of ammunition as he gunned down dozens of his fellow students and staff at Virginia Tech last week, police said on Wednesday.
Police provided new details about how Cho killed 30 other people at Norris Hall on April 16, the deadliest such massacre in modern U.S. history, before killing himself as police raced up the stairs of the classroom building.
http://www.reuters.com/article/topNe...5?feedType=RSS