A 2000 analysis of 102 rampage killings by The New York Times found that most were perpetrated during the day, by educated white men.

However, the Times investigation of this particular style of violence - public rampage killings - turned up an extremely high association between violence and mental illness.

One of the most widely publicized rampage killing involved Colin Ferguson, a black man frustrated by his failed life who blamed white racism for his troubles.

In most ways, rampage killings involving young offenders are no different from those involving adults, The Times found in compiling its database.

Anna Brown, another student in the class, sometimes joked with her friends that Cho was "the kind of guy who might go on a rampage killing."

An analysis of the database found several recurring elements in rampage killings, including some that surprised the experts.

The Ben Strong story shows how chaos and panic can distort the accounts that witnesses give of the rampage killings that periodically horrify the country.

Humiliation, Dr. Dietz said, often precedes rampage killing.

But the other crucial factor in rampage killings, access to guns, can be affected through legislation and regulation.

There are many mysteries behind rampage killings like the one on the Red Lake Indian reservation in Minnesota last week.