A SOBBING killer murdered a love rival who stole her fiance then tried to cover up her evil crimes using her murder mystery knowledge.

Raging Sara McKenzie, 61, savagely attacked 59-year-old Joy Boulton in a warped bid to win back her ex Trevor Dibnah.

The killer, who was a fan of murder mysteries, then tried to put her knowledge into effect as she attempted to cover up the crime.

McKenzie chucked the clothing she was wearing and the weapon used to bludgeon Joy to death.

She also had a bath to remove the blood she was covered in and cleaned it afterwards.

But McKenzie’s assumed insight was blown apart when, in a final act of courage, Joy scratched her killer’s face.

When investigators carried out a post mortem, DNA belonging to the monster was discovered under Joy’s fingernails.

McKenzie broke down as she was convicted of murder and perverting the course of justice.

Guildford Crown Court heard how she had flown into a jealous rage when ex Trevor got engaged to Joy.

McKenzie had previously been in a 13-year “turbulent” relationship with Trevor but he broke things off and moved in with Joy, who he’d been having an affair with.

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She had previously confronted Joy at her home in Ash, Surrey, screaming: “That’s my husband, that’s my man!”

The day after the couple announced their engagement on Facebook, a shed containing Trevor’s possessions was set alight.

McKenzie had also asked her ex “what does she have that I don’t?” three weeks before the murder.

On May 11 this year, the killer showed up at the couple’s home and battered Joy 20 times over the head, causing catastrophic injuries.

After realising police had her DNA, McKenzie then constructed an elaborate web of lies to explain how it ended up under her love rival’s fingernails.

She claimed she had been assaulted during a robbery at her home earlier that day and suggested the female attacker had also gone after Joy.

But jurors saw through her brazen lies and she was convicted in less than three hours.

Paying tribute to Joy, her family said: “We are deeply devastated by this senseless act of violence which has changed our lives forever.

“Joy was a very caring person, who was always ready to help other people whenever she could despite having many health and mobility problems herself. She fought many health problems over the years but always battled on.

“She will be forever missed and always loved. May you rest in peace.”

McKenzie will be sentenced at Guildford Crown Court on Monday.