In the quiet community of Harris, Minnesota, a tragic event unfolded on March 5, 2023, forever altering the lives of a local family. On that Sunday, 68-year-old Denise Lillian Mattson, a White female, was found deceased in her home. She was not alone; discovered alongside her were her husband, Darrell James Mattson, 73, and their son, Kirk Patrick Mattson, 47.
The scene within the Fish Lake Township residence was one of violence, with all three family members having succumbed to multiple gunshot wounds.
The discovery was made after concerned family members requested a welfare check, unable to get in contact with them. The news of the triple homicide sent shockwaves through the small community, prompting a thorough investigation by the Chisago County Sheriff's Office and the Minnesota Bureau of Criminal Apprehension. Investigators quickly assured the public that they did not believe the act was random and that there was no ongoing threat to the community.
As the investigation progressed, a person of interest was identified. This individual was also found deceased, but at a separate location and a day prior to the discovery of the Mattson family. The Hennepin County Medical Examiner's Office would later identify the person of interest as Kenneth George Koslowski, a 39-year-old relative of the victims. Authorities determined that Koslowski had died from a self-inflicted gunshot wound in rural Dakota County.
Forensic analysis provided a critical link between the two scenes. The firearm found with Koslowski was forensically matched to the evidence recovered from the Mattson family's home. Investigators were also able to determine that Koslowski had been in the vicinity of the Mattson residence around the time the homicides were believed to have occurred. While a definitive motive was not publicly released, the investigation concluded that Koslowski was the suspected gunman in the tragic deaths of Denise, Darrell, and Kirk Mattson before taking his own life.
