SAN FRANCISCO — An 18-year-old California university freshman went on an elaborately planned rampage with a hunting knife because he was barred from a study group, authorities said.

Merced County Sheriff Vern Warnke said a two-page “manifesto” detailing Faisal Mohammad’s motive and plans to terrorize and kill several classmates at the University of California, Merced was found on his body Thursday during his autopsy.

Campus police shot and killed Mohammad after the teen stabbed two students, a university employee and a construction contractor shortly after 8 a.m. Wednesday on the rural campus in the farm-rich San Joaquin Valley. The four are expected to survive.

Mohammad’s plan for revenge discussed his anger with being kicked out of the study group, the sheriff said, but he didn’t know why the computer science and engineering major was excluded from the group.

Warnke said Mohammad planned to use plastic ties to bind the hands of his classmates to their desks in his Wednesday morning class. He was then going to call police with a fake distress call and ambush the responding officers.