St. Petersburg police on Monday said a house fire that claimed the lives of a husband and wife last Friday is now being investigated as a murder-suicide.

Charles Nelson, 67, used an accelerant to deliberately set the house on fire while he and his wife, 75-year-old Janet Nelson, were inside, investigators said. Janet Nelson had called police for help but was unable to get out, police said.

Fire officials pulled the Nelsons from the home while battling the flames. Charles was pronounced dead at the scene, while Janet died of her injuries on Sunday.

A neighbor, 76-year-old Pat Ditto, told the Tampa Bay Times that the couple had a dog that also died in the fire.

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The St. Petersburg Police Department had responded to the couple’s home at least twice in the past decade over domestic quarrels, though no one was arrested, police said.

Criminal records cited by the Times show that Charles served 13 years in state prison after pleading no contest in 1993 to sexual battery on a victim under 12.

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An investigation into the Nelsons’ death is ongoing.