A Pennsylvania man will spend decades in prison for stabbing and beating his grandmother to death before setting her body on fire.

George Sisco, 29, was sentenced to 29 1/2 to 60 years in prison on Friday after he pleaded guilty but mentally ill to third-degree murder, arson and terroristic threats in the April 2024 death of 67-year-old Margie Finlay, the Pike County District Attorney’s Office said in a press release.

Crews responded on April 26, 2024, to a fire at Finlay’s home in Milford Township, some 40 miles northeast of Philadelphia. As firefighters began battling the blaze, they found Sisco covered in blood in front of the house. Sisco didn’t respond when an assistant fire chief asked if he needed any help. The defendant walked further into the home and threatened anyone who tried to enter, prosecutors said.

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“She was the devil and I had to do it,” Sisco reportedly said.

Firefighters extinguished the fire and found Finlay dead in the kitchen.

“Sisco admitted to police he killed his grandmother and started a fire in the house, saying the flea medication she was putting on the cat was harmful,” prosecutors said.

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He slashed his grandma’s throat and stabbed her before using a kitchen rag to set her on fire, the Pocono Record reported. Sisco told troopers with the Pennsylvania State Police that the Bible said “in order to kill the devil, he must use the holy spirit and fire.”

An autopsy determined that the cause of death was blunt force trauma and sharp injuries.

A psychological exam originally deemed Sisco, who was diagnosed with schizophrenia, incompetent to stand trial, but a second one cleared him.