Former co-workers called her "Crazy Jill" and neighbors said the woman with the purple Mohawk haircut had a history of mental problems and had tried to commit suicide.

Nineteen-year-old Jillian Robbins, an avid hunter with Army Reserve training, was lying on a tarp under a tree on the Pennsylvania State University campus Tuesday morning when she opened fire with a rifle equipped with a telescopic sight, police said.From her position in front of the student union, Robbins fired five rounds, killing a student and wounding another, both people she said she didn't know, police said.

A student on his way to class saw puffs of smoke from her rifle and tackled her while she tried to reload. When Robbins lunged toward the student, Brendon Ma-lovrh, with a knife, he stepped back and the knife plunged into her leg, police said.

Malovrh, a martial arts-trained aerospace engineering major, quickly took off his belt and tied it around her leg to stem the bleeding as hundreds of panicked students ran across the lawn, one of the campus' busiest areas.

In front of them Melanie Spalla, 19, of Altoona, lay dead.

Nicholas Mensah, 27, was shot first on a sidewalk 100 yards away from Robbins, police said. He was in serious condition following surgery for a gunshot wound to his abdomen.

Robbins, a local resident and high school dropout, was in fair condition, awaiting arraignment on murder charges.

Police have no motive for the shooting, the worst act of violence in the school's 186-year history, and have found no connections between the victims and Robbins.