The family of a man murdered after he started a relationship with a “pathologically jealous” domestic abuser’s ex-partner have said the young couple were “failed by the police”.

Marcus Osborne, 35, has been given a whole life order for murdering Katie Higton and her new boyfriend Steven Harnett in a “ferocious and merciless” knife attack.

Osborne said “Romeo and Juliet can die together now” after the double killing which left Ms Higton, 27, with 99 injuries and Mr Harnett, 25, with 24 wounds including mutilated genitals.

Leeds Crown Court heard that on May 10 last year – five days before the murders – Ms Higton went to Huddersfield police station 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 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 went to the street to spy on her over the following days.

Speaking outside court after the sentencing, Mr Harnett’s twin brother Jordan Harnett said: “The police have failed Steven and Katie – a young couple who had their whole lives ahead of them.

“Now I’m not saying Steven and Katie aren’t here anymore completely because of the failures of both West Yorkshire Police and a ludicrous system we have in place in protecting victims of domestic violence – there is still a monster at the other end of the knife.

“This sorry, pathetic excuse of a man couldn’t contain his jealousy and now her children must grow up without a mummy and my niece now must grow up without her dad.

“The core duty of the police is to prevent crime, so how is a man with a history of domestic violence allowed to walk freely from a police station just a couple of days prior to him murdering my brother and his girlfriend.

“Katie went to the police originally with the intent of making domestic violence allegations against Marcus. She was told to come back tomorrow to give a statement.

“A woman plucking up the courage to speak out about her abuser should be heard there and then.”

Detective Superintendent Alan Weekes of West Yorkshire Police said Osborne’s release was to allow an investigation and a file of evidence to be built for consideration by the CPS, and that “sadly, the measures that were put in place, including bail conditions, were not successful”.

Asked by reporters why Osborne had been released on bail given his history of domestic violence, Mr Weekes said the case was being reviewed by the Independent Office for Police Conduct and that it would be inappropriate to comment further.

The court heard Osborne lay in wait for Ms Higton and attacked her as soon as she came through the door of the house they once shared in Huddersfield, West Yorkshire.

He then used Ms Higton’s phone to pretend to be her and send messages luring Mr Harnett to the house.

Osborne also raped another woman, who 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.

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

She later told police that 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, it was said.

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

The judge, Mrs Justice Lambert, said Ms Higton’s murder was a “merciless and sustained attack on a woman who was completely defenceless”.

She said that during the attack, which started “before (Ms Higton) even got through the front door”, Osborne was heard saying: “I warned you I was going to kill you … this is your fault this is happening.”

The judge said the woman who was held captive in the house described Osborne washing himself between killings, laughing and jeering, later even inviting a neighbour into the living room to see the bodies “as if you were proud of what you had done”.

She imposed 10-year concurrent sentences for the rape and false imprisonment of the other woman in the house.

The judge told Osborne: “There are no mitigating factors in your case other than your guilty plea. There is no psychiatric or other evidence placed before me to explain or help me understand your actions.

“This is a case of such exceptional seriousness that even a very long minimum term would not be a just punishment. What you did that night was horrific.”

A family member shouted “I hope you rot in hell” from the public gallery as Osborne was taken away.