Girlfriend Shauna Hoare, 21, will serve 17 years’ imprisonment for the manslaughter of the 16-year-old.
Trial judge Mr Justice Dingemans was in tears as he started paying tribute to Becky’s family at the end of his sentencing remarks. Matthews, 28, and his girlfriend targeted the 5ft 1in teenager due to their shared dislike of her and their interest in petite teenage girls.
They devised a plan to kidnap Becky from her home in Crown Hill, Bristol, and drove there on February 19 while she was alone.
Detectives say the truth about what happened to Becky that morning may never be known but a pathologist found she died of strangulation.
Becky suffered more than 40 injuries to her body as she bravely fought for her life against porn-obsessed Matthews and his cold-blooded partner.
After her death, the pair dismembered Becky with an £80 circular saw in the bathroom of their squalid home.
They laughed as they watched a parody of a Disney Frozen song, entitled Do You Want To Hide A Body, while Becky’s remains lay just rooms away.
A jury at Bristol Crown Court took just three hours and 27 minutes to convict Matthews of Becky’s murder, while Hoare was found guilty of the teenager’s manslaughter.
Both were convicted of kidnap, perverting the course of justice, preventing a lawful burial and possessing two stun guns.
Passing sentence, the judge said: “I am sure, on the evidence that was adduced at the trial, that the planned kidnap of Becky was for a sexual purpose.
“It is apparent, involving as it did her proposed abduction for a sexual purpose, but in my judgment it does not require a whole life order in the circumstances where Nathan Matthews had been of previous good character and had directed the police after a long delay to Becky’s remains.
“This is not to diminish the loss suffered by Becky’s family.
“Mr Matthews, as a 28-year-old man, will be 61 before he might be considered for release and the reality is that he might never be released.”