Many people who have exploded in violence first made threats or gave warnings that should have raised alarms but did not. That appears to be the case in both the Washington, DC-area sniper killings and the killings last week at the University of Arizona.It has been true of many domestic killings, workplace rampages and other mass murders in the past.In the Washington-area sniper case, it turned out that a friend had warned the FBI in June about John Muhammad and John Lee Malvo, the two men now accused of the shootings.He said they spoke to him of carrying out a sniper attack and killing police.Authorities say they had reservations about aspects of the friend’s account, and Muhammad and Malvo were never interviewed. They are now charged or suspected in 13 killings during an eight-month cross-country crime wave.‘‘I raised the red flag three months ago,’’ said the friend, Harjit Singh. ‘‘I told them what their intention was.’’At the University of Arizona, student Robert S. Flores Jr told a teacher in April 2001 that he was depressed, had thought of suicide and ‘‘might put something under the college’’. It was not clear exactly what he meant, but it was threatening enough for the teacher to go to campus police and file a report.The campus police chief said the department took no action because an administrator and faculty member talked with Flores and felt none was needed. On Monday, Flores walked down the campus with a loaded gun and shot and killed three professors and then himself.
