BISMARCK, N.D. (AP) — North Dakota’s attorney general on Thursday condemned the violent death of an 18-year-old allegedly struck by a man who said he drove his SUV into the victim after the two had a political argument, and he offered to help a county attorney prosecute the case.

The driver, Shannon Brandt, told a 911 dispatcher that he struck Cayler Ellingson early Sunday in McHenry because the teenager was threatening him, and that the teen was part of a “Republican extremist group,” according to a probable cause affidavit.

A breath test after Brandt was arrested Sunday showed his blood alcohol level was above the legal limit to drive, officials said.

The case has provoked an outcry from conservatives, with many going on social media to decry Ellingson’s death and the alleged motive. “Joe Biden’s America!” tweeted Donald Trump Jr.

Investigators said Thursday they have so far been unable to corroborate Brandt’s claims. The 41-year-old man has been charged with criminal vehicular homicide and leaving the scene of an accident that resulted in death.

“There has been no corroboration that this was even politically motivated at all,” North Dakota Highway Patrol Capt. Bryan Niewind told The Associated Press.

Niewind said investigators haven’t found witnesses to the SUV striking Ellingson, but they interviewed several people who were near the two men shortly before. Brandt was the only one to make the claim of a political argument, Niewind said.

According to the probable cause affidavit, Brandt told investigators that he struck Ellingson “because he had a political argument with the pedestrian and believed the pedestrian was calling people to come get him.”

Niewind said the investigation was continuing.

Attorney General Drew Wrigley, in his statement Thursday, called on political leaders to stop the rhetoric that leads to violence. Wrigley, a Republican, also offered to help the Foster County state’s attorney prosecute the case.

Brandt, who was freed on $50,000 bond, did not immediately respond to a message left Thursday at a number listed for him. Ellingson’s parents have not responded to messages.

McHenry is about 150 miles (240 kilometers) northeast of Bismarck.

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