On one night in December 2018, a high-achieving, intelligent maths graduate Joe Atkinson, a man with no history of violence, suddenly became a savage, cold-blooded killer.

Leeds Crown Court heard the breakdown of the couple's relationship had led him to behave like a "Jekyll and Hyde character" in the weeks leading up to the attack. Towards the end of November 2018, Atkinson flew into a jealous rage and attacked Miss Devey Waterhouse's new boyfriend after seeing them out together.

The prosecution described how the attack "was a hint of his brewing jealousy." But at other times friends had described how he had seemed to have accepted the break-up.

Then, in the early hours of December 14, 2018, after a night out drinking with colleagues, Atkinson carried out the "inexplicable" and "harrowing" knife attack on his partner of three y ...