MOSCOW, Idaho — The police arrested a 28-year-old criminology student on Friday and charged him with murder in the brutal killing of four University of Idaho college students who were found stabbed to death overnight in a home near their campus last month.

The man, Bryan C. Kohberger, was taken into custody at his parents’ home in Effort, Pa., where it appeared he had been staying recently, according to Michael Mancuso, an assistant district attorney in Monroe County, Pa.

Mr. Kohberger was pursuing a Ph.D. in criminal justice and criminology at Washington State University, which lies about 10 miles from Moscow, Idaho, where the murders took place. He recently entered the program after graduating in June from DeSales University in Center Valley, Pa., with a master’s degree in criminal justice.

Mr. Kohberger was charged in Idaho with four counts of first-degree murder and was being held without bail in Pennsylvania. An extradition hearing has been scheduled for Tuesday.

“These murders have shaken our community, and no arrest will ever bring back these young students,” the Moscow police chief, James Fry, said at a news conference. “However, we do believe justice will be found through the criminal process.”

The arrest of Mr. Kohberger came nearly seven weeks after the college students were stabbed to death on Nov. 13 in a crime that horrified the small Idaho college town and prompted many students to stay home and finish classes online after Thanksgiving break. Residents had grown increasingly frustrated in recent weeks as a killer remained on the loose, and one victim’s father had begun to publicly criticize investigators.

The police declined to say anything about the suspect’s possible motive, and they said that a long knife they believe was used to carry out the attacks had not been found. But the arrest of a criminology student added another unsettling element to an already macabre case.

The students who were killed — Madison Mogen, 21; Kaylee Goncalves, 21; Xana Kernodle, 20; and Ethan Chapin, 20 — were attacked in at least two separate bedrooms, probably as they slept. The three women lived at the rental house where the attack occurred, while Mr. Chapin was visiting Ms. Kernodle, his girlfriend. Two more roommates apparently slept through the stabbings and did not wake up until several hours afterward.

The police had in recent weeks been searching for the driver of a white Hyundai sedan that they said had been spotted near the victims’ home on the night of the killings. Chief Fry said on Friday that the police had found a car matching that description.

In a post on Reddit from about seven months ago, a user who identified himself as Bryan Kohberger asked people who had spent time in prison to take a survey about crimes they had committed. The survey listed Mr. Kohberger as a student investigator working with two colleagues at DeSales, and it asked respondents to describe their “thoughts, emotions and actions from the beginning to end of the crime commission process.”

B.K. Norton, who was in the same graduate program as Mr. Kohberger, said that he continued attending classes after the killings had occurred and seemed more animated at that time than he had been earlier in the semester.

“He seemed more upbeat and willing to carry a conversation,” Ms. Norton said in an email. She said Mr. Kohberger was interested in forensic psychology.

Ms. Norton said Mr. Kohberger’s quiet, intense demeanor had made people uncomfortable, as had comments he made against L.G.B.T.Q. people.

“He sort of creeped people out because he stared and didn’t talk much, but when he did it was very intelligent and he needed everyone to know he was smart,” Ms. Norton said.

At Mr. Kohberger’s apartment complex in Pullman, Wash., on Friday, several neighbors said they were left unsettled after learning that the suspect had been living so close by and regretted regularly leaving their doors unlocked in the quiet housing development on campus. The complex includes about a dozen apartment buildings, and a children’s playset sat behind the unit where Mr. Kohberger had been living.

Andrew Chua, a graduate student who lived in the same building as Mr. Kohberger, said he briefly met him in August or September. The two spoke about their degrees and where they were from, and Mr. Kohberger had appeared to be excited to continue his studies.

“He was really passionate about what he was doing,” said Mr. Chua.

Another graduate student who knew Mr. Kohberger said he was keenly interested in studying policing. But the student, who spoke on condition of anonymity because of worries about upsetting others in the department, said Mr. Kohberger had few friends at the school. Mr. Kohberger had appeared to want to socialize, the student said, but had made offensive remarks in the past that had left him somewhat isolated.

Students at Washington State University frequently socialize with students from the University of Idaho, which is a 15-minute drive across the state line.

Before moving to Pullman, Mr. Kohberger had spent much, if not all, of his life in the Pocono Mountains region of Pennsylvania.

Casey Arntz, who was one year ahead of Mr. Kohberger at Pleasant Valley High School, said he was known to have a temper and that he did kickboxing, possibly as a way to get his anger out. She said his mother had sometimes worked as a substitute teacher at the high school.

Ms. Arntz, 29, said that she used to occasionally hang out with Mr. Kohberger as part of a group, once hiking a mountain near her parents’ house, but had not seen him since a friend’s wedding in 2017.

According to articles in local newspapers, Mr. Kohberger worked for several years as a security officer with the Pleasant Valley School District, drawing some attention in 2018 for helping another officer save the life of an employee who was having an asthma attack. He left the district in the summer of 2021.

On the night of the killings, the four Idaho students had all spent the night out with friends. Mr. Chapin and Ms. Kernodle attended a party at the Sigma Chi fraternity nearby, while Ms. Mogen and Ms. Goncalves went to a bar called the Corner Club. All four students returned to the home shortly before 2 a.m.

From 2:26 to 2:52 a.m., seven unanswered phone calls were made from Ms. Goncalves’s phone to a former boyfriend. Several calls were also placed to the same man from Ms. Mogen’s phone, the police said. The former boyfriend had not answered the phone because he was sleeping at the time, Ms. Goncalves’s older sister later said.

When the two surviving roommates woke up, they called friends to the house because they believed that one of the women who lived upstairs “had passed out.” When the friends got there, someone in the group called 911 just before noon, and the police arrived to find the victims and what the coroner later described as a bloody scene.

Mr. Chapin’s family welcomed the arrest in a statement on Friday and also acknowledged the long process of grieving that remains ahead for them and other victims’ families.

“We are relieved this chapter is over because it provides a form of closure,” the Chapin family said. “However, it doesn’t alter the outcome or alleviate the pain.”

Ms. Goncalves’s father, Steve Goncalves, who had at one point called the police “cowards” for not releasing more information, commended the police in an interview with Fox News on Friday and said it was the first good news he had heard in some time.

“You can’t even smile, when you have this over your head,” Mr. Goncalves said. “And it feels like a little bit of weight has been relieved.”

Erin Staheli, who has lived in Moscow for about three years and delivers food for DoorDash, said she started crying out of relief when she heard news of the suspect’s arrest. She said she and her boyfriend, who also delivers food for DoorDash, had noticed an increase in orders in the weeks since the crime, which she believed was because people were afraid to go outside.

“It’s been just really scary,” Ms. Staheli said. “Everybody is freaked out.”

At the news conference on Friday, Chief Fry was asked whether the community was safe after so many weeks of fear.

“We have an individual in custody who committed these horrible crimes, and I do believe our community is safe,” he said. “But we still do need to be vigilant, right?”

Rachel Sun reported from Moscow, Idaho, and Pullman, Wash; Nicholas Bogel-Burroughs from New York; and Serge F. Kovaleski from New York. Reporting was contributed by David DeKok, Nate Sanford, Campbell Robertson and Glenn Thrush. Kirsten Noyes contributed research.