Becky Watts' father has revealed he blamed his wife for bringing his daughter's killer into the world - but that he will now defend her "with his life".
Darren Galsworthy spoke last night about the moment he was told his own stepson was responsible for the murder of the 16-year-old.
Nathan Matthews has been found guilty of murdering Becky as part of a sadistic, sexually-motivated kidnap plot with his girlfriend Shauna Hoare.
After he killed her, Matthews brought the girl's body back to his home and dismembered her with a circular saw in a cold-hearted bid to avoid detection by the police.
Anjie Galsworthy, Matthews’ mother and Becky’s stepmother, said she still loved her son and would try to find answers by visiting him in prison, where he could face a whole-life sentence.
"When the police told us about Nathan and Shauna I lost control," Mr Galsworthy told The Sun. "I felt like had been kicked in the chest by a stallion.
“I crumpled and punched the floor and walls - rocking back and forth like a mad man. I blamed Anjie for bringing Nathan into the world and he killed Becky."
Mr Galsworthy said he now vowed to stand by his wife, who told the newspaper her husband "didn't mean" what he'd said. "Anjie is not responsible for the crimes of her son," Mr Galsworthy said.
The pair appeared together on Good Morning Britain on Thursday morning, and Ms Galsworthy revealed she and her husband had defended and trusted Matthews and Hoare and told police “you’ve got it wrong” when they were first arrested.
Speaking about her feelings towards Matthews now, Ms Galsworthy said “the betrayal hurts so much”.
“He's a different person, he's not the child I remember bringing up,” she said.
“I still love him, I just find it hard looking at the monster he's turned into. He's totally different from the child I brought up.”
After a trial lasting more than five weeks, the jury took just over three hours to find Matthews guilty of murdering Becky while Hoare, who prosecutors said was likely present during the killing, was found guilty of manslaughter.
A post-mortem examination found bruising to 40 separate areas of Becky’s body and recorded 19 knife wounds, including slashes to her torso and shoulders, inflicted after her death.
In the hours after the killing, Matthews and Hoare ordered takeaways, joked over text messages and watched an online parody video entitled “Do you want to hide a body?”
Mr Galsworthy told The Sun after the verdicts that he believes the couple’s callous behaviour in the aftermath of the murder shows they could have gone on to kill again, and likened the pair to infamous serial killers Fred and Rose West.
“I think they would have gone on to be the new Fred and Rose,” he said. “They were already texting each other messages saying they had found other pretty girls.”
He added: “They were trying to say it was banter, but it was not. They wrecked our lives and should pay with their own. Give me two nooses and I'd pull that lever.”
Criminologists agreed the murder had similarities to Gloucester serial killers. Stuart Kirby, professor of policing and criminal investigation at the University of Central Lancashire, told the Press Association: “Here you have Matthews as a dominant person in the relationship and she defers to his fantasies and does what he says.
“If they had been successful and gone undetected, who is to say they would not have engineered another incident such as this?”
During a harrowing trial, the court heard how porn-obsessed Matthews and Hoare swapped messages about kidnapping schoolgirls in the months before Becky's death.
Their laptop contained a sickening 17-minute rape video depicting a virgin being attacked in her home, with her rapist placing a hand over her mouth.
The pair will be sentenced on Friday along with Jaydene Parsons, 23, and Karl Demetrius, 30, who owned the shed where Becky's body parts were hidden. The pair admitted assisting an offender.
Matthews faces a mandatory life sentence but could die behind bars, as the sexually motivated murder of a child can carry a whole life order.