Boulton

"There was quite a lot of uncertainty about what we were doing," Dr Frank Boulton, who was working in the west of England at the time, said.

Investigators said the killing happened after McKenzie tried to revive a relationship with Ms Boulton's fiancé Trevor Dibnah, but he refused to get back with her.

Unable to cope with the rejection, McKenzie, of Fairview Road, Ash, went to Ms Boulton's house in Church View with the sole intention of killing her, according to Surrey Police.

Sara McKenzie used a heavy object to inflict fatal injuries on Joy Boulton, 59, at her home in Ash, Surrey, on 11 May.

Crucial evidence was left when Ms Boulton, of Ash, scratched McKenzie’s face.