"Computer science majors took most of their classes from Jim. He was their adviser, and he had a big impact on them," he said.
McDermott added Arnold was a great teacher who "taught the tough stuff" and maintained a sunny disposition — "a person who always had a smile on her face."
Chris Unruh, a student in one of Arnold's pre-calculus classes this fall, said she was a kind instructor who was excited about recently getting two dogs.
"She cared about her students," said Unruh, 18. "She wanted all of them to succeed."
Investigators said Christopher Krumm had recently driven to Casper from Connecticut and had been staying at a local hotel. He had no significant history of encounters with police.
Authorities were uncertain what went awry in his relationship with his father.
"It's difficult to say. I don't think it was very close," Walsh said.
In Vernon, Conn., police Sgt. Timothy O'Connor said officers executed a search warrant at Christopher Krumm's last known address Friday to help authorities in Casper. He didn't know what investigators were looking for or may have found at the home.
"Whatever was recovered will be turned over to Wyoming because it is an active investigation," O'Connor said.
Christopher Krumm's previous addresses include one in the western Massachusetts city of Springfield and others in the Colorado cities of Golden, Fort Collins and Lakewood.
Casper, population 56,000, is about 250 miles northwest of Denver and Wyoming's second-largest city after the state capital, Cheyenne. Wyomingites refer to Casper as the "Oil City" because it is a hub of the state's oil industry.
Casper College is one of seven colleges in Wyoming's community college system. The campus was mostly quiet Saturday morning. Fathers and sons shot hoops in the school gym. A small group of drama students rehearsed a play in the school theater just across the street from the attack.
The building where the attack happened remained cordoned off by police tape that whipped in a brisk wind. A security guard let students back in, one at a time, to retrieve belongings they'd left behind.
Andra Charter, a 20-year-old sophomore, emerged with a coffee mug. She recalled hearing screams outside her biology class before getting word about what had happened.
"As we were walking out, there was a girl screaming, 'There's somebody stabbing Mr. Krumm!'" Charter said.
James Krumm was head of the college's computer science department. He was born north of London and also spent part of his childhood in Germany, according to the college website.
He held degrees from Casper College, a bachelor's degree and MBA from the University of Wyoming and a master's in computer science from Colorado State University.
Arnold held a master's degree in mathematics from the University of Oregon and a bachelor's degree in math from University of California Davis.
The college planned a candlelight vigil and memorial service Tuesday.
Associated Press writers Rodrique Ngowi in Boston and Thomas Peipert in Denver contributed to this report.