By: Devin Fry
MOORHEAD, Minn. (Valley News Live) – An 18-year-old Moorhead man now faces a first-degree premeditated murder charge in the stabbing death of a 14-year-old girl last August, court records show.
The Clay County Attorney’s Office amended the charges against Isaac Arthur Arndt on Monday, adding the more serious first-degree murder count to the existing second-degree murder charge. Arndt pleaded not guilty to both charges during a court appearance Monday before Judge Tammy L. Merkins.
First-degree premeditated murder carries a mandatory sentence of life in prison without the possibility of parole in Minnesota. The second-degree murder charge carries a maximum sentence of 40 years in prison.
The victim’s body was discovered near a bicycle trail on Elm Street and 6th Avenue South in Moorhead on Aug. 20, 2024. She had suffered sharp force injuries to her back, torso and neck.
According to court documents, Arndt went to the Clay County Law Enforcement Center on the evening of Aug. 19, 2024, to report an assault. He claimed an unknown male had cut his hand with a knife while he and the victim were riding an electric scooter at Gooseberry Park.
Hours later, the victim’s mother filed a missing person report. Officers used the SnapChat app’s location feature to locate the girl’s body.
Arndt was arrested after multiple interviews with Moorhead Police detectives and a BCA special agent. He was formally booked at the Cass County Jail on Aug. 20, 2024.
The amended charges come days after Judge Merkins denied a defense motion to suppress statements Arndt made to law enforcement during four separate interviews. In a Jan. 2 ruling, Merkins found Arndt was properly informed of his Miranda rights and voluntarily waived them.
Arndt’s defense attorneys, Lisa Tufts and Steve Bergeson, had argued Arndt never understood his rights and could not knowingly waive them. They cited scientific studies on adolescent brain development and Arndt’s history of trauma from authority figures.
Judge Merkins granted the state’s motion to strike those portions of the defense brief, ruling the information was not properly admitted into evidence. The judge also noted the adolescent brain studies were irrelevant because Arndt is 18 years old and not a juvenile.
Court records show Arndt has 10 prior juvenile delinquency files.
