A murder trial witness whose crucial evidence helped jail three killers has been exposed as a violent rapist.

Shaun Sinclair, 23, is behind bars after terrifying sex attacks on two women.

He raped one after lining up knives on a table and asking her which one she “wanted to die with”.

Sinclair was found guilty following a trial at the High Court in Glasgow.

He returned there two years after his testimony led to three people being jailed for the torture and killing of a vulnerable man in North Ayrshire.

Sinclair was a vital prosecution witness in describing how Scott Blackwood, 30, was brutally attacked before attempts were made to set him on fire.

Allan Nicol, 36, and Thomas Moore, 26, were locked up for murder while Georgina Smith, 22, was jailed for culpable homicide.

Sinclair now faces his own lengthy spell in prison later this month.

The jury heard how he raped an ex-partner and also had sex with her when she was only 15.

Sinclair regularly cheated with other women – but the victim admitted if he told her to “jump off a bridge”, she would have.

He struck after initially ordering her out a flat in Glasgow’s South Side.

When he met her, Sinclair chillingly told her: “You’re going to get a shock when you go in.”

The victim said she knew “something bad was going to happen”. The woman recalled Sinclair punching and trying to choke her. Struggling for breath, Sinclair went on to rape her.

The court heard Sinclair had “battered her black and blue to overcome her will”.

Sinclair then carried out a separate sex attack that day leaving her in tears.

The woman did go to the police – but controlling Sinclair made her withdraw the allegation.

It was put by Sinclair’s lawyer the sexual violence did not happen – but the distressed victim replied: “So, I gave myself two black eyes?”

He went on to rape her again, after leaving her to go and have sex with a neighbour.

She recalled him coming into their Ayrshire flat looking “dead vicious...making gestures as though he was going to kill me”.

The jury heard he trashed the flat before dragging her by the hair yelling: “You are making me do this”.

The woman said Sinclair spoke about “finishing her” as he whipped out a blade.

The court was told he initially put the knife to her throat before “sawing” at her hand.

She said Sinclair stood over her “like a sacrifice” as she feared he was going to plunge the blade into her.

The woman dodged the weapon, but Sinclair still managed to stamp on her face and body.

Not satisfied at leaving the woman battered, a raging Sinclair went on to rape her.

The court heard she was left with “a catalogue of injuries”.

Sinclair also raped another woman at a house in Girvan, South Ayrshire, in January 2013.

He attacked her after smashing up the property. The woman had tried to calm him down, but, instead, Sinclair grabbed her wrists and forced himself on her.

Sinclair was convicted of having unlawful sex, assault and rape against the first woman.

He was found guilty of raping the second woman as well as physically assaulting a third female at a flat in Largs in April 2012.

Sinclair was further found guilty of having sex with another 15-year-old-girl in 2013.

Judge Norman Ritchie QC deferred for reports as he put Sinclair on the sex offenders’ register.