The DNA of the man accused of killing four University of Idaho students was found on a knife sheath at the crime scene, an investigator said in court documents unsealed Thursday. The affidavit written by Moscow, Idaho Police Cpl. Brett Payne was made public just minutes before a court hearing began for the man accused in the Nov. 13 deaths, 28-year-old Bryan Kohberger.

Kohberger was handed over to local authorities in Idaho on Wednesday after a flight from Pennsylvania, where he was arrested at his family’s home in the Pocono Mountains. He is being held in Latah County Jail for allegedly killing Kaylee Goncalves, Madison Mogen, Xana Kernodle and Ethan Chapin in November.

According to the affidavit, agents recovered trash from the Kohberger family residence in Albrightsville, Pennsylvania on Dec. 27 and sent evidence to the Idaho State Lab to be tested.

The next day, a DNA profile obtained from the trash was compared to the DNA profile obtained from the sheath.

“At least 99.9998% of the male population would be expected to be excluded from the possibility of being the suspect’s biological father,” the affidavit said.

Kohberger is charged with four counts of first-degree murder and felony burglary in the closely watched case that has grabbed the nation’s attention and rocked the small college town on the Idaho-Washington border.

His attorney in Pennsylvania, where his parents live and where he was arrested, has said he is eager to be exonerated.

Kohberger faces four counts of first-degree murder and felony burglary for his alleged involvement in the murders, said Latah County, Idaho, prosecutor Bill Thompson during a news conference after his arrest. Before driving cross-country with his father to Pennsylvania, according to Monroe County district attorney Mike Mancuso, Kohberger had just finished his first semester at Washington State University. Located in Pullman, Washington, the campus is roughly 15 minutes from the University of Idaho by car. Kohberger enrolled at the school as a Ph.D. student in criminology and also worked as a teaching assistant there.

He has denied allegations of his involvement in the murders at the University of Idaho, according to Monroe County public defender Jason LaBar, who represented Kohberger in his extradition case. LaBar said during an appearance on NBC’s “Today” show Tuesday that Kohberger’s family was “shocked” by his arrest and the allegations brought against him.

LaBar described Kohberger as calm and intelligent.

“He’s an ordinary man to me, I see no distinct characteristics,” LaBar said. “He’s easy to talk to. He’s aware of the situation. He’s very calm.”

He received a new license plate for his car five days after the murders, according to records released Wednesday.

The licensing documents in Washington State show that the vehicle driven by Kohberger, was a white Hyundai Elantra, the type of vehicle that investigators had been seeking in recent weeks.

The police in Moscow had said that a white Hyundai Elantra from between 2011 and 2013 had been seen near the scene of the crimes on the night of the killings in Moscow, Idaho, on Nov. 13. Kohberger’s car was a 2015 model and registered on Nov. 18, according to the licensing document. A vehicle history report shows the car had previously been registered in Pennsylvania, where Kohberger is from.

He had moved to Pullman, Wash., in recent months and began studying criminology in a Ph.D. program at Washington State University in August. He has said through a lawyer that he expects to be exonerated in the case. His new lawyer did not immediately respond to a request for comment on the license plate records.

On Wednesday, the police in Indiana released new body camera footage showing that, two weeks before Kohberger was arrested, the police there had pulled him over twice in a 10-minute stretch for tailgating. The traffic stops, on Dec. 15, came as Kohberger was driving across the country with his father for winter break in the same car for which he had obtained the new license plate.

During both stops, the suspect’s father mentioned a fatal police standoff that took place that morning near Washington State University, where his son was a student, and told the officer that he and his son had been discussing the “horrifying” incident.

The police shooting that they were discussing does not appear to have any connection to the four fatal stabbings that occurred about a month earlier in Idaho, just across the border from the W.S.U. campus. Kohberger is now charged with four counts of murder in the stabbings.

Stabbed to death. On Nov. 13, Ethan Chapin, Madison Mogen, Xana Kernodle and Kaylee Goncalves, four students at the University of Idaho, were found dead at a home near the campus in Moscow, Idaho. The killings occurred on a typical Saturday night, after two of the victims had been at a bar together and two others had been at a party.

Kohberger was taken into custody at his parents’ home in the Pocono Mountains of Pennsylvania. On Jan. 4, authorities transported him by plane from Pennsylvania, where he had made an initial court appearance the day before, to Idaho. During that hearing, the suspect agreed to be extradited.

The charges. Kohberger faces four counts of first-degree murder and one count of felony burglary. Authorities have yet to detail a motive in the case or how investigators came to identify him as a suspect. Kohberger has said he looks forward to being exonerated, according to his public defender in Pennsylvania.

Kohberger was the driver of the car during both stops, and the new footage is the most that the public has seen of him since he became the subject of intense scrutiny after his arrest. On Wednesday, Kohberger was flown by the police from Pennsylvania, where he was visiting his parents after the road trip, to Idaho, where he stands accused of stabbing four students to death overnight in their home on Nov. 13.

The Pennsylvania State Police plane touched down at the Pullman-Moscow Regional Airport shortly before 6:30 p.m., and Kohberger was booked into the Latah County Jail in Moscow.

Kohberger’s father, Michael Kohberger, visited him in December, and they drove across the country from the W.S.U. campus in Pullman, Wash., to their home in eastern Pennsylvania. During that trip, they were pulled over twice on Dec. 15 for tailgating; in both traffic stops, the officers let the men off with a warning.

There is no indication that the police in Indiana had any idea that Mr. Kohberger would be arrested for the murders, or that they were aware of the police in Moscow, Idaho, saying that a white Hyundai Elantra had been seen near the crime scene on the night of the murders.

During the first stop, at about 10:42 a.m., a deputy with the Hancock County Sheriff’s Department pulled Kohberger and his father over along Interstate 70, just east of Indianapolis. The body camera footage released on Wednesday captured the deputy asking where the two were headed. In response, Kohberger’s father said that they were coming from Washington and had been talking about the police standoff that was unfolding near the Washington State campus that day.

Kohberger’s father told the officer that there had been a “mass shooting.” He was corrected by his son, who said, “We don’t know if it was a mass shooting,” and referred to a SWAT team being called for the standoff. “It’s horrifying,” Kohberger’s father said in the video. That incident involved a man who the police later said had barricaded himself in an apartment and threatened to kill his roommates before a police officer shot him to death.

At another point in the video, the father said, “We’re slightly punchy because we’ve been driving for hours.”

After about three minutes, the deputy said, “Do me a favor and don’t follow too close, OK?” and then returned Kohberger’s driver’s license and let them go.

Just five minutes later, Kohberger and his father were pulled over again, this time by an Indiana state trooper who also said that they were tailgating. The audio from the trooper’s body camera is obscured by traffic noise, but Kohberger and his father could be heard telling the officer that they were just stopped minutes earlier. Again, the father brought up the incident that morning at Washington State. The trooper wished them a safe trip and let them go with a warning.

It was two weeks later, on Dec. 30, that the police in Pennsylvania carried out a predawn raid of Kohberger’s parents’ home, arresting Kohberger on suspicion of carrying out the Idaho killings. They also searched his car and executed a warrant to obtain his DNA, officials said. Kohberger has said through a public defender that he looks forward to being exonerated.

Kohberger had just completed his first semester at Washington State, which is about a 15-minute drive from the crime scene in Moscow. Classmates said he had shown an interest in the psychology of criminals as well as in forensics.