The Grayson County Sheriff's Office says the body of 53-year-old Robert McInchak was located Sunday night at his home in Denison.
Sgt. Rickey Wheeler says McInchak died of an apparent self-inflicted gunshot wound. An autopsy has been ordered in Dallas.
McInchak had faced trial Monday over the April 2011 death of 58-year-old Shellman Smith Jr. of Denison.
Authorities say Smith's dog was shot by McInchak after the pet allegedly wandered into the man's yard near the Denison Country Club.
Investigators say Smith left the course to see what happened and was fatally shot during a confrontation on McInchak's property.
The dog survived.