A man has been found guilty of murdering the teenage girl who called him her father, after she claimed that he had sexually abused her "over a number of years".
Bernadette Walker, 17, was last seen alive on July 18 last year when 51-year-old Scott Walker, who was not her biological father, collected her from his parents' house in Peterborough, Cambridge Crown Court heard.
However, he did not bring the teenager back to their home in Century Square, in Millfield, that morning.
Her mother, Sarah Walker, and Scott Walker's former partner, was also found guilty of two counts of perverting the course of justice by sending messages from the teenager's phone and providing the police false information.
The day Bernadette was last seen alive, Scott Walker's mobile phone activated cell sites in the Dogsthorpe and Gunthorpe areas, and at just before 11.30am, it was disconnected from the network and didn’t reconnect for an hour-and-a-half.
Prosecutors said that Scott Walker killed her to "prevent her pursuing her allegations of sexual abuse any further".
Her body has not been found despite police searches.
Scott Walker said that Bernadette, known as Bea, ran away from his car when he stopped the vehicle, but jurors rejected his account.
The prosecution said Bernadette told her mother, 38-year-old Sarah Walker, on July 16 last year that Scott Walker had sexually abused her "over a number of years" but that Sarah Walker did not believe her daughter's allegations.
Scott Walker told jurors that Bernadette's allegations of sexual abuse were "untrue".
The prosecution said that Bernadette was sent to stay with Scott Walker's parents overnight the next day "while things calmed down a little", with Scott Walker collecting her on July 18, when she was last seen alive.
Sarah Walker reported Bernadette as missing to police in the early hours of July 21.
Lisa Wilding QC, prosecuting, said that Scott Walker formed an "unholy alliance" with Bernadette's mother, his ex-partner Sarah Walker, to cover up the girl's death, over the next seven weeks sending messages from Bernadette's phone to give the impression she was still alive.
Sarah Walker admitted sending messages from Bernadette's phone after she disappeared and by providing false information to the police relating to her disappearance.
Scott Walker told the court that Sarah Walker had feared the involvement of social services over the allegations against him.
Sarah Walker had previously admitted perverting the course of justice without knowing Bernadette was dead and to cover up sexual allegations against Scott.
However, the jury found her guilty on two counts of perverting the course of justice with the knowledge that her daughter was dead.
Meanwhile, Scott Walker was also found guilty of two counts of perverting the course of justice.
Ms Wilding said that Scott Walker's phone, "which was usually in regular use", was off between 11.23am and 12.54pm on July 18.
"The prosecution say that in that hour and a half he killed Bea," she said.
Ms Wilding said that when Scott Walker's phone reconnected to the network at 12.54pm the first call he made was to Sarah Walker, which lasted for more than nine minutes.
"The only sensible conclusion that can be drawn from that telephone call is that Scott Walker told his wife that he had killed Bernadette and needed her help, immediately, to cover up Bea's disappearance and death, and to buy them both time to work out what should happen next," said Ms Wilding.
"The story they concocted in that call, and which both relied on from that moment on, even until now, was that Scott had stopped the car on the short drive home to confront Bea about her allegations, that Bea jumped out of the car when he pulled over and that she ran off.
"Then, that Scott tried and failed to run after her and so returned home without her.
"From that moment on, Scott and Sarah Walker - Bea's own mother and father - were joined, the prosecution say, in an unholy alliance, designed and intended to mislead, to divert and to pervert the inevitable investigation into the disappearance and ultimately the death of Bea Walker."
Sarah Walker was not married to Scott Walker but had changed her surname to Walker by deed poll.
At the time of Bernadette's disappearance, Scott and Sarah Walker were living at the same address but Sarah Walker was in a relationship with another man.
Scott Walker said in evidence that he considered the possibility that Bernadette's allegations and disappearance may have been a "plan" to get him "out of the house".
Sarah Walker did not give evidence during the six-week trial.
After the verdict was announced, Detective Inspector Justine Jenkins, from the Beds, Cambs and Herts Major Crime Unit, said: “I am pleased we have been able to get justice for Bea after what has been such tragic circumstances.
“I just hope now we may get the answers we need to be able to find her and lay her to rest. If anyone has any information about this investigation which may help us find Bea, please get in touch.
“We may never know the truth about what Scott did and why, but we do know Bea had made allegations of abuse against him.
“My plea to anyone who may have been subjected to abuse is to speak to us. Bea thought she could confide in her own mother, who should have been able to protect her, but instead she met a tragic end.”
Scott Walker claimed that when Bea ran away from his car, she had left her rucksack behind.
However, police discovered that instead of going straight to collect her that morning, he had gone to a lock-up garage owned by his parents in Walton.
In the following 48 hours, both he and Sarah Walker made multiple trips to the lock-up as well as to Cowbit, a rural area of Lincolnshire, in the dead of night.
This was while passwords on Bea’s social media accounts were changed and messages sent to friends and family to make it look as though Bea had simply run away from home.
The allegations Bea had made about being sexually abused by her father were passed to police via a social worker on July 22.
On 10 September, Scott was arrested for this and allegedly coercively controlling Sarah. The following day, the investigation became a murder enquiry.
Bea’s rucksack was found in the Walton lock-up and a diary found inside. An extract read, “Told my mum about my dad and the abuse. She called me a liar and threatened to kill me if I told the police. What kind of parent wouldn’t believe their daughter?”
Meanwhile, extensive searches by specially trained officers continued for many weeks, but Bea’s whereabouts remain unknown to this day.
DI Jenkins said: “We know Bea was without her mobile phone when she left the family home on July 17.
“Despite this, a number of messages via text and social media were sent from Bea’s phone, by both Scott and Sarah, to make it look as though she was still alive and not wanting to go home. This would then explain their failure to report her missing for several days.
“After three days of Bea having been ‘missing’, Sarah contacted us via webchat to ask for advice and eventually called 101 to make a formal missing person report.
"It was clear nothing had been done to make sure Bea was safe, just a very long line of lies and deceit which grew by the day."
A date for sentencing has been set for September 10, 2021.
Information about the investigation can be passed on to police either online or by calling 101.
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