The president of Yale University says more safety precautions are being taken after the bizarre killing last month of a graduate student.

Richard Levin's comments came in an e-mail sent this week to faculty and staff members. He says improvements are being made to emergency communications in isolated indoor and underground areas.

Levin also says temporary employees will now undergo background checks.

Twenty-four-year-old Annie Le was killed Sept. 8 in the basement of a Yale lab building with restricted access. Lab worker Raymond Clark III is charged with murder.

Levin did not mention retired Yale employee John Petrini, who was arrested without incident last month when he took a rifle to campus while upset about his benefits.