Today's killings of at least 29 people on the campus of Virginia Tech is among the worst school shootings in U.S. history. Here's a look at some other notable attacks on U.S. campuses:
Oct. 2, 2006: A gunman took about a dozen girls hostage, killing at least three of them, at a one-room Amish schoolhouse in Pennsylvania's Lancaster County, police said. The shooter was among the dead, and a number of people were injured.
Sept. 29, 2006: 15-year-old Eric Hainstock brought two guns to a school in rural Cazenovia, Wis., and fatally shot the principal, a day after the principal gave him a disciplinary warning for having tobacco on school grounds, police said.
Full coverage continues on "World News With Charles Gibson," "Nightline," "Good Morning America," and an ABC network special Tuesday at 10 p.m. EDT
Sept. 27, 2006: Duane Morrison, 53, took six girls hostage at Platte Canyon High School in Bailey, Colo. Morrison, sexually assaulting them and using them as human shields for hours before fatally shooting one girl and killing himself.
Aug. 24, 2006: Christopher Williams, 27, went to an elementaryschool in Essex, Vermont, looking for his ex-girlfriend, a teacher. He couldn't find her and fatally shot one teacher and wounded another, police said. Williams also killed his ex-girlfriend's mother, according to authorities. He shot himself twice in the head ater the rampage and was arrested.
March 21, 2005: Sixteen-year-old Jeff Weise shot and killed five schoolmates, a teacher and an unarmed guard at a high school on the Red Lake Indian Reservation in Minnesota before taking his own life. Weise had earlier killed his grandfather and hisgrandfather's companion.
Nov. 22, 2004: Sixteen-year-old Desmond Keels is accused of fatally shooting one student and wounding three others outside Strawberry Mansion High in Philadelphia. The attack apparently was over a $50 debt in a rap contest. Keels is set to stand trial on murder charges later this month.
April 24, 2003: 14-year-old James Sheets shot and killed the principal in the crowded cafeteria of a junior high school in south-central Pennsylvania, before killing himself.
May 26, 2000: 13-year-old Nathaniel Brazill killed his English teacher on the last day of classes in Lake Worth, Fla., after the teacher refused to let him talk with two girls in his classroom. He was convicted of second-degree murder and is serving a 28-year sentence.
April 20, 1999: Students Eric Harris, 18, and Dylan Klebold, 17, killed 12 students and a teacher and wounded 23 before killing themselves at Columbine High School in Littleton, Colo.
May 21, 1998: Two teenagers were killed and more than 20 people hurt when a teenage boy opened fire at a high school in Springfield, Ore., after killing his parents. Kip Kinkel, 17, was sentenced to nearly 112 years in prison.
May 19, 1998: Three days before his graduation, an honor student opened fire at a high school in Fayetteville, Tenn., killing a classmate who was dating his ex-girlfriend. Jacob Davis, 18, was sentenced to life in prison.
March 24, 1998: Two boys, ages 11 and 13, fired on their Jonesboro, Ark., middle school from nearby woods, killing four girls and a teacher and wounding 10 others. Both boys were later convicted of murder and can be held until age 21.