Police at first struggled to find a motive for the murder, as there was no evidence of any robbery having taken place, only signs of a struggle. It was only after a wide appeal for information that a local shoe-shiner, 34 year old John Rawsthorne was apprehended on 20th March. Rawsthorne was known as 'soft Johnny' by local youths and was described in newspapers as being a 'half wit' and of 'weak intellect'. Various witnesses came forward to say they had seen him acting suspiciously in the area on the day of the murder, while he also watched William's funeral from a distance, telling one of the ladies who attended that if he had been ten minutes earlier he could have saved him.
Rawsthorne told police that he was living in the Liverpool workhouse at the time of the murder and couldn't have been in the vicinity, but this was proved to be untrue. Witnesses said they had seen him in a farmer's field near the cemetery and also outside Breck Road station on the day of the murder, whilst his landlady said he claimed to have been watching Everton play Sheffield Wednesday at Goodison Park.
At his trial Walton Gaol’s medical officer described Rawsthorne as a ‘mental degenerate’ who wouldn't be able to understand evidence. His defence submitted that he was not capable of distinguishing the quantity of his actions but the jury decided he knew the difference between right and wrong as he carried out his crime. Rawsthorne was found guilty of murder but with a recommendation for mercy and his death sentence was subsequently commuted to life imprisonment by the Home Secretary.