Two years into his incumbency on Exmoor the murder of Anna Maria Burgess, aged 6, took place. She died at the hand of her father, William Burgess, who gave out the story that Anna had gone to live with her grandmother in Porlock Weir. Thornton checked with the grandmother, who confirmed that she had not seen the child. Without a body Thornton could prove nothing but Burgess fled and Thornton personally rode into Wales, where he had tracked him down. He brought him back, and had him held in Exford whilst he awaited permission from the authorities to drain the flooded, and defunct, Wheal Eliza mine, a mile and a half along the Barle Valley from Simonsbath village. Local rumour had it that lights had been seen over the mineshaft and sheep-stealers had found an empty grave upon the moor. It took until the October for permission to be granted to pump the shaft and, in the November, a local young man volunteered to be lowered down it. 360 feet down he found a bundle and, when it was recovered to the surface, Thornton unwrapped it to discover the remains of the child. Burgess was tried at Taunton Assizes, found guilty of the murder, and sentenced to hang.