MOUNT HOREB, Wis. — A 21-year-old man is facing a tentative homicide charge in connection with the “cold, calculated and extremely violent” homicide of Nicholas Day in January, an official said.

Dane County Sheriff Dave Mahoney said Riley Berg, of Mount Horeb, was arrested on a tentative charge of first-degree intentional homicide in Day’s death.

Riley Berg is in custody. Still no motive. Still no known relation. Sheriff’s office is asking for information from public (no matter how small you think the information could be). #News3Now — Gabriella Bachara (@GabbyBachara) February 14, 2020

Day’s body was discovered by a passerby on Jan. 15. At first, the incident was reported as a hit-and-run death, but an autopsy confirmed Day suffered a gunshot wound and had suffered several lacerations.

During the news conference Friday, Mahoney called Day’s killing a “cold, calculated and extremely violent” homicide.

Mahoney said Day was shot while he was out for a run, then Day suffered multiple “significant” cuts to his neck. The killing happened in a narrow window of time.

The sheriff’s office said “the motive for the killing is still unclear, and at this point, a connection between the victim and the suspect is unknown.”

Day was a “son, a loving father and a U.S. Veteran,” Mahoney said. “This tragedy will live on for this community for a long time. It has specifically torn apart many families. I call upon our community to offer compassion and help healing. It is tragic in many ways, and I know that it will take a long time for the community, and for these families, to heal.”

Investigators are asking for anyone who knows Berg, who may have information on a connection to Day, or who has information on Berg’s activities and behavior before and after Day’s death, to call the tip line at 608-284-6900.