Later that year, he moved to Yorkshire and assumed the alias of John Palmer. While he was staying at an inn, local magistrates became suspicious of "Palmer" and made enquiries as to how he funded his lifestyle. Suspected of being a horse thief, "Palmer" was imprisoned in York Castle, to be tried at the next assizes. Turpin's true identity was revealed by a letter he wrote to his brother-in-law from his prison cell, which fell into the hands of the authorities. On 22 March 1739, Turpin was found guilty on two charges of horse theft and sentenced to death; he was executed on 7 April 1739.