From his cell, Turpin wrote to his brother-in-law, Pompr Rivernall, who also lived at Hempstead. Rivernall was married to Turpin's sister, Dorothy. The letter was kept at the local post office, but seeing the York post stamp Rivernall refused to pay the delivery charge, claiming that he "had no correspondent at York". Rivernall may not have wanted to pay the charge for the letter, or he may have wished to distance himself from Turpin's affairs, and so the letter was moved to the post office at Saffron Walden where James Smith, who had taught his younger schoolmate Turpin how to write while they were at school, recognised the handwriting. He alerted JP Thomas Stubbing, who paid the postage and opened the letter. Smith travelled to York Castle and on 23 February identified Palmer as Turpin. He received the £200 (about £ as of ) reward originally offered by the Duke of Newcastle following Turpin's murder of Thomas Morris.