A suspect has been arrested in the murder of Robert Tester, the nephew of Sen. Jon Tester, D-Mont., in Washington state.

According to the Great Falls Tribune, Spokane County Sheriff’s Major Crimes detectives arrested 22-year old John A. Radavich in Spokane Valley with the assistance of U.S. Marshals on Thursday.

On Sept. 6, Robert Tester, 35, was found dead and lying in a pool of blood 18 miles south of Spokane, Washington. Deputies found his daughter uninjured.

A wood-splitting ax stained with blood was found nearby and bags of marijuana were found near the body. Robert Tester’s mother said her son grew marijuana for dispensaries.

During the investigation, it was discovered the Montana Democrat’s nephew had a 17-year-old girlfriend whom he reportedly assaulted the day before he was killed.

A friend of Radavich revealed to detectives a phone call he had recorded of a man identified as Radavich admitting to killing Robert Tester for assaulting the girlfriend.

Radavich was reportedly an ex-boyfriend of the 17-year-old. The investigation is ongoing.