Two tenured art professors have resigned from the University of California, Los Angeles, because the school refused to suspend a graduate student who may have used a gun during a classroom performance art piece.

Chris Burden (search) and Nancy Rubins (search), internationally known artists who taught at UCLA for more than two decades, filed their retirement papers Dec. 20.

"They feel this was sort of domestic terrorism. There should have been more outrage and a firmer response," said Sarah Watson (search), a director at a Beverly Hills gallery that represents the couple.

In the brief performance on Nov. 29, the student appeared to point a loaded handgun at his head and pull the trigger, a student and law enforcement officials told the Los Angeles Times.