Idaho Murder Suspect Had Been a Student of the Criminal Mind

The classmate recalled one instance in which Mr. Kohberger began explaining a somewhat elementary criminology concept to a fellow Ph.D. student, who then accused him of “mansplaining.” A heated back-and-forth ensued and the Ph.D. student eventually stormed out of the classroom, leaving behind her laptop and coffee, he said.

Mr. Kohberger was also a teaching assistant in a criminal law class during the fall semester, said Hayden Stinchfield, 20, one of the students in that class. He said that Mr. Kohberger often cast his eyes down while speaking in front of the students, not looking at the class directly, giving the impression that he was uncomfortable.

Students said Mr. Kohberger had a strong grasp of the subject matter but was a harsh grader, giving extensive critiques of assignments and then defending the lower marks when students complained as a group. Later in the fall, roughly around the time of the killings, Mr. Stinchfield said Mr. Kohberger seemed to start giving better grades, and the assignments that once had his feedback scrawled across every paragraph started coming back clean.

“At a certain point he stopped leaving all the notes,” he said.

At the time, a growing team of investigators from local and state agencies, as well as more than 60 agents from the F.B.I., had descended on Moscow. Forensics investigators combed the house for physical evidence, including D.N.A., and searched fruitlessly for a murder weapon.

Officials pleaded for tips and videos, while thousands of internet sleuths around the country suggested an array of people as the likely culprit: a former boyfriend of one of the victims, a man who was with two of the victims when they got a meal from a food truck, two roommates who were in the home when the killings occurred but apparently slept through them.

None of the online discussion groups identified Mr. Kohberger. It is not clear how or if he knew the victims.

The police had tried to tamp down rumors by ruling out several people as suspects, though the accusations were flying so fast that it at times appeared they could not do so quickly enough. They withheld nearly all details of the investigation, raising frustrations and prompting some people, including some relatives of the victims, to wonder publicly whether the police were up to the task.