ATLANTA - The killings at Virginia Tech university overnight will stir fresh US debate over gun control and what drives people to go on shooting rampages through schools and colleges.
The killer's identity and motive were not immediately known, but as the death toll rose, it became the deadliest campus shooting in US history, the latest in a string of spree killings.
It was the worst since Charles Whitman went to the top of a tower at the University of Texas on August 1, 1966, and opened fire. He killed 15 people, including his mother and wife the night before, and wounded 31 others.
Last October, a gunman shot 10 Amish girls at a one-room schoolhouse in Pennsylvania, killing five before turning the gun on himself.
In April 1999, teenagers Eric Harris and Dylan Klebold, armed with guns and homemade bombs, killed 12 fellow students and a teacher at Columbine High School in Colorado in a long-planned spree.
School shootings have prompted changes to school safety rules and sparked debate over the availability of guns.
They also have prompted an outpouring of academic studies on the causes of stress, depression and violence in young people and novels such as the award-winning We Need to Talk About Kevin by Lionel Shriver, about a school massacre.
People who commit killings in schools and colleges are sometimes motivated by a specific grievance against that institution or people within it, said Nadine Kaslow, a professor and chief psychologist at Emory School of Medicine.
They are sometimes mentally ill and may equally be reacting to a trauma, either real or imagined, that they have suffered, and decide to take that trauma out on everyone else, Kaslow said in an interview.
"Some of these people -- I don't want to use the word 'snap' -- but they just go over the edge. All the rest of us have a conscience that says: 'don't do this,'" she said stressing she was new to the Virginia Tech case.
The way in which the media play up cases such as Columbine may make the idea of committing such a crime to achieve notoriety attractive to certain individuals, she said to explain why such killings appear more prevalent in the United States than in other Western countries.
Advocates of wider gun controls said the availability of guns in the United States had made it easier for people to commit murder everywhere, including in schools and colleges.
"What have we done as a nation in the 8 years since Columbine about this problem? We compound the trade of the day by our failure to deal with the proliferation of guns in our country," said Paul Helmke, president of the Brady Centre to Prevent Gun Violence.
Helmke said that since Columbine, which happened eight years ago this week, there had been no new legislation on control of guns and he said a ban on assault weapons was allowed to expire in September 2004.
Advocates of gun freedom such as the National Rifle Association argue that the right to bear arms is enshrined in the US constitution and dispute efforts to link the incidence of gun crime with access to firearms.
Many recent studies have looked at student-on-student violence and its causes and after Columbine intense scrutiny focused on the lives and backgrounds of the two gunmen, who committed suicide.
It also focused on school bullying, social cliques and the potential effects of the music they listened to and the video games they played. Experts also looked for ways to spot warning signs of violence.
Kaslow said that violence in US schools was a bigger problem than was reported because of the high incidence of bullying, hitting and sexual offences. Shootings were just an extreme form of that violence, she said.
"We are bombarded with violent images in our culture. We have a culture of violence here (in the United States). Kids will go home and watch this on TV," she said.