Not only a criminal.
As a professor, one of the key points of his job, as of any academic, is to insist that students produce original work, that they take credit only for work that is original to them, and that they cite their sources completely and accurately. As a professor, he is obliged to teach this not only as part of his lectures and grading protocols, but to teach it by example.
He has violated one of the most basic principles of his profession. He has earned dismissal.