A Wyoming college professor slain by bow and arrow in his classroom died at the hands of his son, who also killed the woman who shared his father's home before stabbing himself to death, police said on Saturday, a day after the double murder and suicide.
Police also said the father, Jim Krumm, 56, who taught computer science at Casper College, managed to stagger to his feet despite being "mortally wounded" from the arrow shot to his head, and grappled with his son, allowing his students to flee the classroom unharmed.
Authorities found the attacker, Chris Krumm, 25, and his father dead or near death in the third-floor classroom. The son had driven a large knife into his father's chest after they struggled, then stabbed himself numerous times, according to the Casper Police Department.
Authorities later found Heidi Arnold, 42, who taught mathematics at Casper College and lived with the elder Krum, stabbed to death at their home.
Police said she had been slain by the son that morning before he set out for campus.
Chris Krumm arrived at the school armed with a bow-and-arrow weapon called a compound bow - a type of crossbow - and two knives, all wrapped together inside a blanket, police said.
Casper police initially said the victims' injuries were caused by a sharp-edged weapon. They revealed additional details of the slayings in a statement and news conference on Saturday.
"I can't even imagine what the students in that room had gone through," Police Chief Chris Walsh told reporters, explaining that students watched horrified as Chris Krumm stepped into the classroom and unleashed an arrow at his father from his crossbow.
The students had all safely fled the classroom before the final moments of the bloodbath, he said.
Police offered no possible motive for the killings, but the assailant and Arnold knew each other, and the attacks appeared to have been planned in advance.
Walsh said the suspect, who had lived most recently in Vernon, Connecticut, and was not a student of the community college, had come to Casper days earlier and was staying at a local motel.
Jim Krumm was born in England and also lived in Germany while growing up, then attended the University of Wyoming and Colorado State University, where he earned a master's degree in computer science, according to a biography posted on the Casper College website.
Arnold earned a bachelor's degree from the University of California at Davis, and master's of science from the University of Oregon.
Casper College, where some 5,000 students are enrolled, canceled classes for the rest of Friday and made counselors available to students.
Casper, with a population of about 55,000, is the second-largest city in Wyoming after Cheyenne, the state capital.