Larue told investigators that while watching YouTube videos Tuesday evening, he grew paranoid that someone would rape or harm his mother, an arrest affidavit said.
The affidavit said he grabbed a shotgun, but it was not working, so he grabbed a handgun and began pacing on the ground floor of the home.
Limbaugh was awakened and walked downstairs, where Larue said he shot Limbaugh and his bulldog in the head twice each, the affidavit said.
"Larue advised he killed his mother because he was protecting her from individuals who were supposedly coming to harm her," the report said.
Larue told detectives that he ignited his mattress with a lighter, boarded a boat in the backyard and rowed across a lake to a bonfire at another home, where he was told to leave before running into a wooded area shirtless, the affidavit said.
Detectives said Larue told them that he walked to a Winn-Dixie grocery store and asked a homeless man wearing an eye patch for a shirt before walking to the district office, where he surrendered to deputies.
Larue was booked into the Marion County Jail on charges of first-degree arson of a dwelling and homicide. He is being held without bail.
The death and the fire remain under investigation.