Guilty Plea Entered in Grisly Murder on Blackfeet Indian Reservation

Jason Avery Mattson pleaded guilty to killing an unidentified man, taking a woman hostage in March 2020

By Andy Viano

A 30-year-old Browning man admitted to killing and partially dismembering a tribal member on the Blackfeet Indian Reservation in March 2020, days before taking a woman hostage for several hours and telling a dispatcher he “liked to kill.”

Jason Avery Mattson, who is also a member of the Blackfeet Tribe, entered two guilty pleas in U.S. District Court in Great Falls on March 30, and faces a significant prison term despite reaching a plea agreement with prosecutors. Mattson pleaded guilty to one count of second-degree murder and one count of kidnapping. He is scheduled to be sentenced by Judge Brian M. Morris on June 24.

According to court filings, the body of a man identified as John Doe was discovered in a “moderately remote” area of the reservation on March 3, 2020. The Beacon confirmed the victim’s identity with federal law enforcement but is not identifying him. According to a Glacier County coroner, Doe was decapitated and had both hands cut off at his wrists.

During law enforcement’s investigation of the murder, a witness came forward to say Doe asked for a ride in late February and requested to be taken to several different locations, eventually getting dropped off at Mattson’s trailer. Doe had showed the witness a large bag of methamphetamine before getting out of the car and seemed “scared,” according to the witness. Doe entered Mattson’s trailer without knocking.

One week after the discovery of Doe’s body, on March 10, Mattson called Blackfeet Law Enforcement Services and told a dispatcher that he wanted to confess to Doe’s murder, providing the victim’s full name, identifying himself as Jason Mattson, and telling the dispatcher he was armed with a knife and a gun.

When law enforcement arrived at Mattson’s location to arrest him, Mattson called dispatchers back and said he had taken a hostage, identified in court documents as Jane Doe. Mattson claimed to be holding her at knifepoint and said he had taken a hostage “because he killed John Doe.” When a dispatcher asked Mattson about his state of mind, “he said that he was going to kill Jane Doe” and at one point added that “he liked to kill.” Mattson held the woman hostage for four hours before she escaped and Mattson was taken into custody.

At the time of the murder, Mattson was on federal probation from a 2017 conviction for assault with a dangerous weapon. In that case, Mattson and his older brother, Jerry Mattson III, had originally been charged with three counts, including assault with intent to commit murder. According to an offer of proof filed along with a plea agreement in that case, Jason Mattson shot a man in the neck in June 2013 while the victim and his brother were fighting, then proceeded to fire at the man while he hid in some trees a short while later. Mattson was sentenced to four years in prison in that case and released on Oct. 18, 2019.

The FBI, Bureau of Indian Affairs and Blackfeet Law Enforcement Services all investigated the murder of John Doe.