A Ph.D. student who went from studying crime scenes and serial killers to being charged in the mysterious murders of four Idaho college students was set to plead guilty on Wednesday in a deal that would spare him from the death penalty.

The agreement reached between prosecutors and the suspect, Bryan Kohberger, was a surprise twist in a case that has spawned books, documentaries and years of social media speculation since November 2022, when four University of Idaho students were stabbed to death in the middle of the night in a home near campus.

But while the deal was set to resolve the question of whether Mr. Kohberger, 30, would be convicted, it also raised significant new ones. Among them were whether a motive would ever be revealed, since Mr. Kohberger had no known connection to the victims, and whether Mr. Kohberger would discuss how he had carried out the crime and evaded arrest for more than six weeks.

The plea hearing, scheduled for 11 a.m. local time in Boise, will be a turning point in a grisly drama that was only increasing in intensity as the trial, which had been set to begin in August, drew nearer.

At the time of the crimes, Mr. Kohberger was a few months into a criminology program at Washington State University, about a 15-minute drive from the crime scene in Moscow, Idaho. He had moved there from Pennsylvania, where he was raised and where he had recently completed a master’s program in criminal justice, during which he had surveyed criminals about their emotions and thoughts while they carried out their past crimes.

Investigators have said he drove around the victims’ home on King Road before entering the house and going into two bedrooms around 4 a.m., where he fatally stabbed four college students: Kaylee Goncalves, 21; Madison Mogen, 21; Xana Kernodle, 20; and Ethan Chapin, 20.