A professor emeritus at Missouri State University was stabbed to death Wednesday night in his home, and a fellow instructor was arrested in connection with the murder.

Officials said that the professor and the instructor knew each other and taught within the same department, but a motive has not been identified.

The victim, Marc Cooper, was a professor emeritus of history. He taught at Missouri State from 1980 to 2014 and continued to work on scholarship after he retired. His wife was also stabbed and was taken to the hospital with non-life-threatening injuries.

Edward M. Gutting (at right, in photo from Greene County Prison) was apprehended at the Coopers’ home and is now in jail. Local police said Thursday afternoon that he hadn’t yet been charged, as they were still trying to understand why the attack took place.

Gutting’s title is instructor of modern and classical languages. A Missouri State spokesperson said that Gutting worked in the history department from 2011 until this year, some of that time overlapping with Cooper. He has been placed on administrative leave.

Professors killing other professors is highly unusual but not unprecedented. Amy Bishop, a former assistant professor of biology at the University of Alabama in Huntsville, killed three of her colleagues and wounded three more at a faculty meeting in 2010, after she was denied tenure.

Ethan Schmidt, an assistant professor of history at Delta State University in Mississippi, was shot dead on campus by a fellow faculty member in 2015. The killer, Shannon Lamb, an instructor of geography who in his faculty profile described himself as an expert in the geography of crime, also was accused of murdering his girlfriend, Amy Prentiss, some 300 miles away from Delta State. He killed himself during a manhunt.

In June, William S. Klug, an associate professor of mechanical and aerospace engineering at the University of California, Los Angeles, was killed in his office by a former graduate student who reportedly accused the professor of stealing a computer code. The killer, Mainak Sarkar, later shot himself. Authorities found what they called a “kill list” in his home, which included the name of another faculty member, who was left unharmed, as well as that of Ashley Hasti, Sarkar's estranged wife, who was found dead in her Minnesota home.

Colleagues of both Missouri State professors involved in Wednesday’s crime expressed grief and shock. “During his nearly 35 years on faculty, [Cooper] was an active scholar, publishing several articles on the cuneiform tablets of ancient Iraq,” Victor Matthews, dean of the College of Humanities and Public Affairs, said in a statement.

Jason Jolley, chair of the modern and classical languages department, said he was surprised and saddened by the news, according to The Springfield News-Leader. Gutting was reportedly scheduled to teach four general education courses this fall.