Telling police he believed he was “doing God’s work,” a 73-year-old Port Jefferson man was arrested Thursday — after he poured motor oil onto the rear entrance of the Kingdom Hall of Jehovah’s Witnesses in Mount Sinai the day before.

The incident was captured on video surveillance equipment at the hall, police said.

Suffolk County police said William Frank Kelly, of 17 Sheep Pasture Road, told them he had attended a function at the Hall Tuesday night celebrating “a memorial of Jesus Christ’s death” and that, at that function, he had questioned the beliefs of Jehovah’s Witnesses — and was asked to leave.

He told police that “believing he was doing God’s work,” he then returned to the hall early Wednesday morning and poured two quarts of motor oil onto the rear entrance.

Kelly was charged with fourth-degree criminal mischief as a hate crime and is scheduled for arraignment Friday in First District Court, Central Islip, police said.

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