Partner guilty of cannabis murder

Stephanie Barton was found with multiple stab wounds

A drug-user has been found guilty of murdering his girlfriend who he stabbed to death after becoming convinced she was part of a plot to kill him.

Marc Middlebrook, 26, of Larkspur Croft, Boston in Lincolnshire, attacked Stephanie Barton, 32, with three types of knife in December 2007.

Middlebrook had denied murder on the grounds of diminished responsibility, claiming mental health problems.

He was remanded in custody and will be sentenced on Thursday.

The jury heard how Middlebrook had smoked cannabis since the age of 16, increasing his use after meeting Ms Barton, an accountancy student.

Prosecutors challenged his claims of diminished responsibility by arguing he made his problems worse by "stubbornly" persisting in his use of cannabis - despite doctors advising him to stop.

William Harbage QC told the court Middlebrook's "abnormality of mind" was "self-inflicted".

When interviewed, Middlebrook claimed he stabbed her to death because he feared for his own life.

The jury took less than an hour to return its verdict.