8. In what is the all-time deadliest school shooting in U.S. history, Virginia Tech University student Seung-Hui Cho, 23, shot up the campus on two separate attacks just hours apart on April 16, 2007, killing 32 people before turning the gun on himself. Cho had been diagnosed with a mental illness and the school was found responsible for not alerting campus residents and staff after his first shooting rampage. 10. One L. Goh, 43, killed seven people at Oikos University in California near the Oakland International Airport and was arrested just an hour later.