Sir William Rae, the Lord Advocate, followed a regular technique: he focused on one individual to extract a confession on which the others could be convicted. Hare was chosen and, on 1 December, he was offered immunity from prosecution if he turned king's evidence and provided the full details of the murder of Docherty and any other; because he could not be brought to testify against his wife, she was also exempt from prosecution.[92][96] Hare made a full confession of all the deaths and Rae decided sufficient evidence existed to secure a prosecution. On 4 December formal charges were laid against Burke and McDougal for the murders of Mary Paterson, James Wilson and Mrs Docherty.[97][98]