The fatal stabbings of four students at the University of Idaho has shaken the US college town of Moscow, a small community nestled in the rolling agricultural hills of the Palouse region that had not seen a murder for five years.
The November 13 killings seemed to mystify police, adding to the tension in town as the weeks went by without a break in the case.
Then, on Friday, a suspect was arrested more than 4,000 kilometres away in Pennsylvania.
Bryan Christopher Kohberger, 28, was taken into custody in the early morning by the Pennsylvania State Police at a home in Chestnuthill Township, authorities said.
Latah County, Idaho, prosecutor Bill Thompson said investigators believe Mr Kohberger broke into the students' home "with the intent to commit murder".
DNA evidence played a key role in identifying Mr Kohberger as a suspect in the killings and authorities were able to match his DNA to genetic material recovered during the investigation, a law enforcement official said.
In recent days, federal investigators had been watching Mr Kohberger.
He is a PhD student in the Department of Criminal Justice and Criminology at Washington State University, which is near the University of Idaho. He also is a teaching assistant for the university's criminal justice and criminology program, according to a WSU's online directory.
Federal and state investigators are now combing through Mr Kohberger's background, financial records and electronic communications as they work to identify a motive and build the case, the law enforcement official said. The investigators are also interviewing people who knew Mr Kohberger, including those at WSU, the official said, speaking on the condition of anonymity.
Mr Kohberger is being held without bond in Pennsylvania and will be held without bond in Idaho once he is returned, Mr Thompson said.
The affidavit for four charges of first-degree murder in Idaho will remain sealed until he is returned, the prosecutor said. He is also charged with felony burglary in Idaho. An extradition hearing is scheduled for Tuesday (local time).
The students — 21-year-olds Kaylee Goncalves and Madison Mogen and Xana Kernodle and Ethan Chapin, both 20 — were stabbed to death at a rental home near campus in Moscow, a town of about 25,000 people near the Washington state border.
Moscow Police chief James Fry said investigators are still looking for a weapon. He was emotional as he announced the arrest at a news conference on Friday, calling the victims by their first names.
Tips began pouring in after law enforcement asked the public for help finding a white Hyundai Elantra sedan seen near the home around the time of the killings.
In addition to the DNA evidence, authorities also learned Mr Kohberger had a white Hyundai Elantra, the official who spoke anonymously said.
The two universities are partners in several academic programs and students sometimes attend classes and seminars or work at the neighbouring schools.
University of Idaho President Scott Green wrote in a memo to students and employees on Friday evening that the Idaho school had no record of him.
In the memo, Mr Green said the arrest was "the news we have been waiting for".
"The crime has nevertheless left a mark on our university, our community and our people," Mr Green wrote.
Goncalves, 21, of Rathdrum, Idaho; Mogen, 21, of Coeur d'Alene, Idaho; Kernodle, 20, of Post Falls, Idaho; and Chapin, 20, of Conway, Washington,
The four victims were members of the university's Greek system and close friends, and three of them were housemates. Ms Kernodle and Mr Chapin were dating and he was visiting the house that night.
Autopsies showed all four were likely asleep when they were attacked, were stabbed multiple times and suffered defensive wounds.
Ben Roberts, a graduate student in the criminology and criminal justice department at WSU, described Mr Kohberger as confident and outgoing, but said it seemed like "he was always looking for a way to fit in".
"I had honestly just pegged him as being super awkward." Mr Roberts said.
Mr Roberts started the program in August — along with Mr Kohberger, he said — and had several courses with him. He described Mr Kohberger as wanting to appear academic.
"One thing he would always do, almost without fail, was find the most complicated way to explain something," he said.
Safety concerns had also led the University of Idaho to hire security to escort students across campus.
"To describe it as a relief is pretty much spot on," said Brian Wolf, a sociology professor who specialises in criminology and social control.
"It's still sombre, because we lost four members of our University of Idaho family, but it's safe to say we will probably all sleep better tonight."
AP/ABC
