GREAT FALLS — Jason Avery Mattson of Browning admitted in federal court in Great Falls on Tuesday to murdering a man and holding a woman hostage by knifepoint on the Blackfeet Indian Reservation.
Acting U.S. Attorney Leif Johnson said in a news release that Mattson, 30 years old, pleaded guilty to second-degree murder and to kidnapping as charged in an indictment.
Court documents state that during the investigation, law enforcement officers identified a witness that had seen "John Doe" on February 28, 2020. He had approached the witness and asked for a ride. He was acting spooky, but Doe told the witness that he wouldn’t let anything happen to them. Doe asked to be taken to several locations and finally asked to be dropped off at Mattson’s trailer. Doe showed the witness a baggie with a large amount of meth in it. The witness described Doe as seeming scared. When he was dropped off at the Mattson trailer, Doe walked in without knocking.
Several days after Doe’s body was found, agents interviewed Mattson’s father at his trailer. Unbeknownst to law enforcement, Mattson had been staying at the trailer. Mattson had been on absconder status with United States Probation at the time. The night after agents were at the trailer, Mattson set the trailer on fire. The room where Mattson had been staying was completely destroyed.
Court documents state that on March 3, 2020, officers responded to a moderately remote corner of the Blackfeet Reservation after the discovery of a body. The body was partially obscured by plywood that had been placed on top and showed obvious signs of homicide. The body was identified as "John Doe" and family was notified of his death.
An autopsy confirmed the manner of death as homicide and determined that Doe sustained blunt force injury to his back and extremities and that there was evidence on the neck consistent with strangulation or blunt force injury.
On March 10th, Mattson called Blackfeet Law Enforcement Services (BLES) Dispatch. In recorded calls, he told the dispatcher that he wanted to make a confession - that he had killed Doe. When asked for clarification, he provided Doe’s full name, and said that he had killed him. When asked his name, the caller identified himself as Jason Mattson. He told dispatch that he had a knife and a gun. While officers were responding to the residence, Mattson called again and told dispatch that he had taken a hostage.
He was holed up in the bedroom of a family member’s home and was holding a hostage at knifepoint. When asked who he was holding hostage, he identified Jane Doe by name. When asked why he was holding her hostage Mattson said it was because he killed John Doe. When asked what was going through his mind, he said that he was going to kill Jane Doe. At one point, Mattson said that he liked to kill. The dispatcher could hear the hostage crying and begging to be let go.
Mattson held Jane Doe hostage by knifepoint for approximately four hours before she was able to escape. Shortly after she escaped, Mattson was taken into custody.
Mattson faces a sentence of up to life in prison and a $250,000 fine. Chief U.S. District Judge Brian Morris presided, and scheduled sentencing for June 24. Mattson remains in custody.