It was after one of his aforementioned hunting trips that Turpin’s downfall began. On 2nd October 1738, ‘Abraham Green saith that John Palmer of Welton… with a gun kill[ed] a tame fowl which did belong to Francis Hall of Brough… and did throw the fowl into the fields of Elloughton… [John Robinson] reprimanding the said John Palmer concerning the same, he the said John Palmer did threaten to shoot this informant’. Several witnesses complained to local magistrates, who committed Turpin to keep the peace and provide sureties whilst they conducted an investigation. Turpin refused, and was imprisoned at Beverley, Yorkshire.
Things now gathered momentum. Turpin rode the horse he had stolen from Thomas Creasy, and stabled it at a nearby tavern. Meanwhile, the magistrates’ investigations led them to become suspicious of John Palmer. Although Palmer ‘lived like a gentleman’, no one knew how he made a living, and his movements followed a regular, determined pattern. Whenever he returned from Lincolnshire, he always brought back several horses and large sums of money, which led to suspicions that he was either a highwayman or horse-stealer. Turpin responded to the allegations by claiming he was a butcher from Long Sutton, Lincolnshire.
Enquiries were made at Long Sutton, but it transpired that Palmer, though a resident, was not a butcher, and was actually suspected of sheep- and horse-theft. Thus what had started as a trivial matter was now a major investigation: horse-theft had been a capital offence since 1545, and was punishable by death. Turpin was moved from the prison for petty-criminals at Beverley to York Castle. Meanwhile, Thomas Creasy by chance found out that a horse-dealer had been arrested, and had stabled a gelding matching the description of his missing horse. He found his missing horses in the vicinity of Beverley.
In addition to the suspicions of Palmer at Long Sutton, the justices now had a specific charge against him for horse-theft. Additional evidence was taken from the man to whom Turpin sold the mare and foal, Captain George Dawson. He revealed how Palmer had sold him the animals on the street during a chance encounter, claiming that they were bred in Lincolnshire. Crucially, the horse-dealer also explicitly stated that the animals belonged to him. Although it was unlikely that a horse-stealer would be executed for a first offence, one with charges of murder, robbery, and assault was a different matter.