The Devil's Rejects

On May 18, 1978, Texas Sheriff John Quincey Wydell and a large posse of State Troopers issue a Search and Destroy mission on the Firefly family for over 75 homicides and disappearances over the past several years. The family arm themselves and fire on the officers. Rufus is killed and Mother Firefly (Leslie Easterbrook) is taken into custody, while Otis and Baby escape. They steal a car, and after killing the driver, they go to Kahiki Palms, a run-down motel.
While at the motel, Otis and Baby take a band called Banjo and Sullivan hostage in their room, and Otis shoots the roadie when he returns. Meanwhile, Baby's father, Captain Spaulding, decides to rendezvous with Baby and Otis. En route, his truck runs out of gas and he assaults a woman before stealing her car. Back at the motel, Otis sexually assaults Roy's wife Gloria and demands Adam and Roy come with him on an errand.
Otis drives his two prisoners to a place where he buried weapons. While walking to the location, the two prisoners attack Otis, but he bludgeons Roy and cuts Adam's face off. Back at the motel, Adam's wife Wendy tries to escape out the bathroom window. When Gloria attempts to rebel, Baby kills her. Wendy runs out of the motel, but is caught by Captain Spaulding, who knocks her unconscious. Otis returns, and all three leave the motel together in the band's van.
The motel maid comes to clean the room, and discovers the murder scene. The maid enters the bathroom, where she sees "The Devil's Rejects" written on the wall in blood, and is startled by Wendy, who is accidentally killed when she runs out to the highway to seek help. Wydell calls a pair of amoral bounty hunters â the "Unholy Two" â Rondo and Billy Ray, to help him find the Fireflys. While investigating, they discover an associate of Spaulding's named Charlie Altamont. Wydell begins to lose sanity when Mother Firefly reveals that she murdered his brother. After having a dream in which his brother asks him to avenge his death, Wydell stabs Mother Firefly to death. The surviving Fireflys gather at a brothel owned by Charlie, where he offers them shelter from the police.
After he leaves the brothel, Wydell threatens Charlie to give up the Fireflys. With the help of the "Unholy Two", the sheriff takes the family back to the Firefly house where he tortures them, using similar methods they used on their own victims. He nails Otis' hands to his chair, and staples crime scene photographs to Otis's and Baby's stomachs, then beats and shocks Captain Spaulding and Otis with a cattle prod, and taunts Baby about the death of her mother.
Wydell sets the house on fire and leaves Otis and Spaulding to burn, but lets Baby loose outside so he can hunt her for sport. Charlie returns to save the Firefly family, but is killed by Wydell. Baby gets shot in the calf of her left leg, brutally horse-whipped, and then strangled by Wydell. Tiny suddenly arrives and intervenes, killing Wydell, and saving the Firefly family. Otis, Baby, and Spaulding escape in Charlie's 1972 Cadillac Eldorado, leaving behind Tiny, who walks back into the burning house. The trio drives, badly injured and seemingly humbled by their experience, towards a police barricade. Refusing to surrender, Otis drives them towards the barricade, firing their guns, and all three are shot to death by the police.

Question: Who set the house on fire?
Answer: Wydell