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A mother and a boyfriend she had known for only a matter of months have been jailed for life for murdering her two-year-old daughter.

In the weeks before her death on September 14 last year, Isabelle suffered 21 broken bones before a final ‘massive head injury’ was inflicted upon her.

This was consistent with being ‘violently shaken’ and her head ‘impacting a hard and unyielding surface such as a wall or hard floor,’ Teesside Crown Court heard.

On the morning of Isabelle’s death, Simpson had been caring for her alone while Walker slept.

At some point during this time she was violently sexually assaulted.

He then left Walker’s property in Thornaby, Teesside, on his bicycle.

When Walker woke in the afternoon after a night of heavy drinking and found Isabelle barely conscious and bleeding from a wound consistent with sexual assault, rather than call an ambulance, she smoked a cigarette and then used Google to search: ‘Why would my toddler be bleeding?’

Alexandra Walker, 25, was found guilty of the murder of Isabelle and child cruelty

Harrison Simpson, 22, was convicted of murdering and sexually assaulting the toddler, as well as child cruelty

An hour later she finally called her stepfather who immediately told her to dial 999.

Despite an ambulance arriving within a minute, Isabelle could not be saved and died in the early hours of the following morning.

Sentencing the pair today, the judge, Ms Justice Norton, said it was difficult to describe their course of conduct as 'anything other than sadistic.'

She said that Walker's actions in failing to call the emergency services when Isabelle clearly required medical attention was 'because you believed she was already dead and were working out what to do to save your own skin.'

Judge Norton said that, before Simpson arrived in Walker's life, Isabelle was a 'happy and healthy child.'

She added: 'There has been a wall of silence, lies and obfuscation built up surrounding the last few weeks of Isabelle's life before her murder.

'Harrison Simpson, you have been silent throughout. You have said nothing in [police] interview or at trial. Before you came into Isabelle's life she was a happy, healthy and thriving child.'

Turning to Walker, the judge said she was a 'liar and fantasist who wanted attention.'

She said: 'Whether or not it was attention seeking that led you to commit these offences or some misguided loyalty to Harrison Simpson.... you never said you were forced into acting as you did and you had significant support from parents, the health visitor, the nursery and GP but you made no attempt to get their support or help.'

Simpson was jailed for life with a minimum term of 27 years and 231 days in prison.

Walker was jailed for life with a minimum term of 21 years and 48 days in prison, with time on remand awaiting trial taken into account for both defendants.

Simpson, wearing a grey tracksuit jacket, and Walker, in a black blazer and white shirt, stared blankly ahead as the sentences were delivered.

In the run-up to her suffering the fatal skull fracture on September 13 last year, Isabelle suffered 21 broken bones, internal tears from violent sexual assaults and had 97 soft tissue injuries from being tightly held and shaken.

Tragically, shortly before her death, the toddler was sent home from hospital after doctors overruled other staff's concerns for the child.

Eleven days before her murder, she was reluctantly taken to a GP and then hospital by her mother with a fractured leg.

Staff at North Tees Hospital in Stockton, Co Durham, did not want to allow Isabelle to leave with her, fearing potential abuse.

Little Isabelle suffered 21 broken bones, internal tears from violent sexual assaults and had 97 soft tissue injuries from being tightly held and shaken

After the jury returned guilty verdicts, Isabelle's father, Josh Welsh, said: 'It means the world to me that we have justice for Isabelle'

Walker had waited two weeks to seek treatment despite Isabelle struggling to walk. She claimed the young girl must have hurt her leg when it got caught in her cot.

When concerns were raised at the hospital on September 2, Walker became 'argumentative' and angry - lunging at a nurse who raised the issue of safeguarding.

The mother warned the nurse that speaking to a safeguarding team was 'totally unnecessary'.

Doctors on a paediatric team eventually overruled the concerns and Isabelle was allowed to leave with Walker.

A health visitor was asked to speak to Walker because of the hospital's initial concern - but she did so over the phone and Walker convinced her that everything was above board.

Less than a fortnight later paramedics found Isabelle lying motionless at the foot of the stairs.

Tragically, the same nurse who raised safeguarding concerns was on duty when Isabelle returned to hospital and could not be resuscitated.

The nurse said the child was 'covered from top to toe in bruises'. In court, Walker blamed Simpson for the injuries. Simpson declined to give evidence but his barrister said Walker was responsible for Isabelle's death.

The trial heard the couple met on Facebook Dating in the summer of last year but within a short time he was living at her house in Thornaby, Teesside.

The pair would regularly drink and smoke cannabis together.

Soon, however, Simpson began showing an unhealthy interest in Isabelle, bathing her alone unprompted and always making sure Isabelle was with Walker, rather than wishing to see his girlfriend alone.

This prompted Walker to search the Sex Offenders’ Register for his name and question whether he was a paedophile.

After deliberating for seven hours, jurors found Simpson and Walker guilty of murder and child cruelty.

Simpson was also found guilty of assault by penetration of a child under 13. Walker was cleared of the same charge.

Detective Chief Inspector Steve Chatterton, of Cleveland Police, said: ‘Isabelle suffered catastrophic injuries at the hands of the very people who should have loved her, cared for her and protected her.

‘Her life was cruelly taken in the most tragic and heartbreaking circumstances.

‘She should have had a lifetime of opportunities ahead of her. Instead, Walker and Simpson robbed Isabelle of her future and deprived her family of watching her grow up and achieve those milestones that so many take for granted.’