Administrators at the University of California at Riverside canceled several exams and a Friday-night graduation ceremony for business majors after finding two homemade firebombs and receiving several threats.

According to the Los Angeles Times, the two firebombs were discovered early Friday morning after firefighters were called to the campus because of a tree fire near the site of the ceremony. Later, two letters appeared that included threats directed at the commencement.

University officials said other graduation ceremonies scheduled for Saturday, Sunday, and Monday would go forward, but with tightened security. —Lawrence Biemiller