A Dawson County jury has convicted a man of strangling his ex-wife and dumping her body in the Yellowstone River in 2008.
Walter Martin "Marty" Larson Jr. was found guilty Monday of deliberate homicide and tampering with evidence in the death of Susan Casey.
Casey was last seen outside her Glendive apartment early April 12, 2008. Her body was found three weeks later.
Larson was arrested in Arizona in February 2012 after a four-year investigation.
Assistant Attorney General Brant Light says Larson began "spiraling out of control" when he learned of a romantic relationship Casey was having.
The Billings Gazette reports the 42-year-old Larson testified he had nothing to do with her disappearance and death.
Judge Richard Simonton says a sentencing date will be set after a pre-sentence investigation.