Becky Watts's killers had the potential to be the "new Fred and Rose West", her father has said.
The 16-year-old was brutally murdered in a sexually motivated kidnap plot devised by her stepbrother Nathan Matthews and his girlfriend Shauna Hoare.
Speaking after the pair were convicted by a jury on Wednesday, Becky's father Darren Galsworthy and his wife Anjie Galsworthy, who is Matthews's mother, said they could have gone on to kill again.
"I think they would have gone on to be the new Fred and Rose," he told The Sun. "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 the Wests.
Stuart Kirby, professor of policing and criminal investigation at the University of Central Lancashire, said: "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?"
Elizabeth Yardley, associate professor of criminology at Birmingham City University, said the pair had "a similar bond to the one that developed between Fred and Rose West".
Becky suffered more than 40 injuries as she fought for her life in her pink and white bedroom at her home in Bristol.
Porn-obsessed Matthews, 28, is facing life in jail after being convicted of Becky's murder at Bristol Crown Court.
Hoare, 21, who was branded "calculating and cold-blooded" by police, was found guilty of manslaughter and trying to cover up the crime.
The couple, who fantasised about taking a teenage girl to the attic of their squalid home less than two miles away, had packed a kidnap kit in the boot of their Vauxhall Zafira.
They let themselves into her family's semi-detached house in Crown Hill while Becky was alone during the morning of February 19.
The truth about what happened to Becky, who was suffocated by Matthews, may never be known.
Over three days her body was dismembered into eight parts by Matthews and Hoare, using a saw, a kitchen knife and a screwdriver.
The pair even watched a parody of Disney's Frozen, entitled Do You Want To Hide A Body, as Becky's remains lay in their bath.
Former TA soldier Matthews promised a friend £10,000 to store Becky's body parts - carefully wrapped in cling film, bags and tape and packed with cat litter and salt - in his garden shed.
Police searched the outhouse in the early hours of March 3, discovering the truth when a detective unwrapped Becky's severed right hand.
During a harrowing trial, the court heard how 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.
A post-mortem examination found that after death Becky suffered 16 stab wounds and a long slash wound to her stomach.
Her mother Tanya Watts, grandmother Pat Watts and brother Danny Watts said Becky was "like a tornado, hurricane and sunbeam all at once".
"She came into your life and made you feel alive," they added.
Matthews and Hoare will be sentenced on Friday 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.