(CNN) A graduate student at Washington State University was arrested Friday in his home state of Pennsylvania in last month's killings of four University of Idaho students in their off-campus home -- a brutal attack that rattled a small college town, authorities said.
A criminal complaint charging Bryan Kohberger, 28, with four counts of murder in the first degree, as well as felony burglary, was filed Thursday, Latah County Prosecutor Bill Thompson said in a news conference Friday afternoon in Idaho.
Authorities narrowed their focus to Kohberger after tracing his ownership of a white Hyundai Elantra seen in the area of the killings, according to two law enforcement sources briefed on the investigation. Kohberger's DNA has also been matched to genetic material recovered at the off-campus house where the students were stabbed to death, according to the sources.
Genetic genealogy helped investigators identify the suspect, a source with knowledge of the case said. DNA found in Idaho was taken through a public database to find potential matches for family members, the source said. Once potential family matches were found, subsequent investigative work by law enforcement led to the identification of Kohberger, according to the source.
The suspect drove across country in the white car to his parents' house, according to another law enforcement source. "Sometime right before Christmas we were zeroing in on him being in or going to Pennsylvania," the source told CNN.
An FBI surveillance team from the Philadelphia field office had been tracking him for four days in the area where he was arrested, according to the sources.
While he was being watched, investigators from the Moscow Police Department, the Idaho State Police homicide bureau, and the FBI worked with prosecutors to develop sufficient probable cause to obtain the warrant. Once the arrest warrant was issued, the Pennsylvania State Police and the FBI made the arrest.
Moscow Police Department Chief James Fry said at the news conference an Elantra has been located, but investigators are still looking for the knife used in the killings. He didn't reveal any details about the case, including when the suspect became the focus of the investigation or whether he knew the four students who were killed.
"These murders have shaken our community and no arrest will ever bring back these young students," Fry said. "However, we do believe justice will be found through the criminal process."
Fry said it was a very complex, extensive case.
"We developed a clear picture over time," he said, "(but) be assured that the work is not done. This is just started."
Authorities at the news conference asked the public to keep calling the tip line with information.
After the suspect returns to Idaho, a probable cause affidavit used to obtain the arrest warrant will be unsealed.
Records show Kohberger was arraigned Friday morning in Pennsylvania, and he has a court hearing on extradition January 3. Thompson said the suspect is being held without bail, and he is being represented while in Pennsylvania by a public defender.
Because the suspect was arrested in Pennsylvania, he has the opportunity to waive extradition and return to Idaho voluntarily. If he chooses not to return voluntarily, Moscow police will initiate extradition proceedings through the governor's office, Fry said.
"If we do that, it can take a while for him to get here," he said.
According to a news release from Washington State University, Kohberger completed his first semester as a PhD student in the school's criminal justice program earlier this month.
Elizabeth Chilton, chancellor of the university's Pullman campus, said the school's police department assisted Idaho law enforcement officials in the execution of search warrants at Kohberger's office and his apartment.
A CNN team in Pullman, which is only about 9 miles from the site of the killings, saw law enforcement activity at an apartment complex where graduate students live.
"We also want to extend our deepest sympathies to the families, friends, and Vandal colleagues who were impacted by these murders," Chilton said. "We will long feel the loss of these young people in the Moscow-Pullman community and hope the announcement today will be a step toward healing."
In a post removed from Reddit after Kohberger's arrest was made public, a student investigator associated with a DeSales University study named Bryan Kohberger sought participation in a research project "to understand how emotions and psychological traits influence decision-making when committing a crime."
"In particular, this study seeks to understand the story behind your most recent criminal offense, with an emphasis on your thoughts and feelings throughout your experience," the post said. It is unclear who wrote the questions for the survey.
One of the principal investigators of the study, a professor at DeSales University, in Pennsylvania, declined to comment on the matter.
Kohberger graduated in 2020 with a bachelor's degree, according to a school spokesperson, in June 2022 Kohberger completed his "graduate studies for the Master of Arts in criminal justice program," the spokesperson said.
The suspect also graduated from Northampton Community College with an associate degree in arts and psychology in 2018, a spokesman for the school in Pennsylvania said.
The November 13 killings riveted the nation and shocked the small college town of Moscow, its first murder in seven years. The case prompted fear and anxiety in the community and student body, and questions mounted about the pace of the police investigation.
Moscow resident Erin Staheli became emotional while expressing her relief at the news of the arrest.
"It's just been very scary not knowing who's out there," Staheli said, noting the fear which has permeated the town of almost 26,000 residents for weeks. "I had doubts that the killer would be caught because it's been so long, you know."
Staheli praised the work of the police agencies and FBI for the arrest. "I knew that they would, but it's just taking so long, and I'm so happy for their families and everybody that's been worried that all the students, everybody that may not have come back to school," she said.
The arrest comes a day after police said they have received about 20,000 tips through more than 9,025 emails, 4,575 phone calls, and 6,050 digital media submissions, while having conducted over 300 interviews.
The slain students -- Kaylee Goncalves, 21; Madison Mogen, 21; Xana Kernodle, 20; and Kernodle's boyfriend, Ethan Chapin, 20 -- were likely asleep when they were each stabbed multiple times in the early morning hours, authorities have said. Some of the victims had defensive wounds, a coroner has said.
"Today's news of arrest is a welcome one. It's relief to our university, our community and our extended Vandal family," University of Idaho President Scott Green said at the news conference. "The outpouring of support over the past six weeks help sustain us during the most trying time."
The home where the killings occurred will be cleaned up but remain an active crime scene under police control, authorities said Thursday. Work at the property was halted Friday due to a court order, the police chief said.
Moscow police say they have worked with a property management services company to remove "potential biohazards and other harmful substances used to collect evidence," the update said. The home will be turned over to the property management company.