A domestic disturbance in Green Valley, Arizona, ended in a fatal shooting in the early hours of a Tuesday when deputies found 53-year-old Russell Santos with a gunshot wound to the chest. Santos was pronounced dead at the scene. The residence belonged to 67-year-old Bradley Lewis, who had a domestic relationship with Santos and reportedly called 911 to report that he had shot him. News reports also described the victim as the suspect’s stepson.

Investigators arrested Lewis on suspicion of second-degree murder and booked him into the Pima County jail. The motive has not been released. Anyone who knew Russell Santos or who may have information about what happened that night is asked to come forward.