McDermott described James Krumm as a "real kind and gentle-mannered guy" who was well-respected by his students.
"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.