A “much-loved mother” told police her ex-partner had threatened to kill her if she ever got another boyfriend days before she and her new love interest were murdered in a “ferocious and merciless” knife attack, a court heard.

Marcus Osborne forced his way into the house he once shared with Katie Higton, armed with a knife, while she was on a cinema date with Steven Harnett.

Leeds Crown Court heard Osborne, 35, lay in wait for Ms Higton and launched a brutal attack on her as soon as she came through the door.

Prosecutor Jonathan Sandiford KC said Ms Higton, 27, suffered 99 injuries during the fatal assault “against which she was effectively defenceless, although she put up a courageous struggle”.

Osborne then used Ms Higton’s phone to pretend to be her and lure Mr Harnett, 25, to the house in Huddersfield, West Yorkshire.

He then murdered Mr Harnett, who was left with 24 knife wounds, including mutilated genitals, the court heard.

Another woman who was in the house told police Osborne said: “Romeo and Juliet, they can f****** die together now,” and moved the bodies so they were side by side before remaining in the house for several hours.

He then raped the other woman, whom he had held captive in the house overnight, at knifepoint.

The court heard four children were in the house during the murders, which happened in the early hours of May 15 last year.

Mr Sandiford said: “The defendant committed a premeditated and brutal double murder motivated by sexual jealousy, a desire to exercise control over Katie Higton, an unwillingness to accept her decision to leave him and her freedom to form a relationship with another man.”

Ms Higton had been in a relationship with Osborne for five years, but left him in early May last year after an assault on April 28 which was “the last straw”.

She later told police the relationship had become “coercive, controlling and physically abusive” in the last two years and that she had been regularly assaulted, including one incident when he threw a cat at her, the court heard.

Osborne also has convictions for violent offences against two previous partners in 2011 and 2012, Mr Sandiford said.

Ms Higton went to Huddersfield police station on May 10 to make a complaint about Osborne, and spoke to a member of police staff over the phone later that day. She was visited by an officer on May 11.

During phone calls to the police Ms Higton said Osborne had told her “he would slit her throat if she said what he had done” and that “if she ever got a boyfriend he would kill them both”.

On May 12 Osborne was arrested on suspicion of domestic violence offences and bailed with conditions not to go back to their home, but spied on her over the following days before taking a taxi to the house on the night of the murders.

The court heard he found out about the developing relationship between Ms Higton and Mr Harnett by hacking into her Snapchat account.

A victim personal statement by Ms Higton’s mother Nicola McAlister, read in court, said Osborne was “a monster of the worst kind”.

Ms McAlister wrote: “I no longer live, I simply exist in a tortuous world without my baby.

“I am tormented every second of every day that I draw breath.”

Osborne has previously pleaded guilty to two counts of murder, and the false imprisonment and rape of the other woman in the house.

He did not react to the details of the offences during the first day of his sentencing hearing on Thursday. He repeatedly looked towards the public gallery, where members of Mr Harnett’s family could be heard sobbing.

Mr Sandiford said the prosecution would argue that Osborne’s crimes are serious enough that a whole-life order should be imposed.