Image copyright Avon and Somerset Police Image caption Nathan Matthews (middle) and Shauna Hoare (right) were found guilty of killing Becky Watts (left)

Becky Watts' stepbrother and his girlfriend have been jailed for killing the teenager in a sexually-motivated kidnap plot and dismembering her body.

Nathan Matthews was sentenced to 33 years for murdering Becky in a violent struggle in her bedroom. Shauna Hoare was given 17 years for manslaughter.

Judge Mr Justice Dingemans said the couple's understanding of proper conduct was "corrupted and warped".

Becky's mum Tanya said she had been in a "living nightmare" since her death.

In an impact statement read out at Bristol Crown Court, she said the fact her daughter had been both murdered and mutilated was "like the worst of all horror movies".

In court

Jon Kay, BBC West of England Correspondent

This five-week trial has been filled with emotion and drama, but the final five seconds were perhaps the most extraordinary.

As Mr Justice Dingemans came to the last few words of his sentencing comments, his voice faltered, his eyes filled with tears and he stopped speaking.

He then closed his file of papers and left the stunned courtroom.

He had just been paying tribute to the dignity that Becky's family had shown throughout this harrowing case.

Many of them told me afterwards that they were deeply moved to see a senior judge appearing to sympathise and empathise with their situation.

Describing seeing her in the mortuary, Ms Watts said: "The image of Becky there, with a bandage around her little wrist trying to cover up the cut marks; that image haunts me."

Matthews, 28, suffocated 16-year-old Becky at her home in the St George area of Bristol on 19 February while trying to kidnap her. Hoare, 21, who was pregnant at the time, was at the address.

Judge Dingemans said he was sure the planned kidnap "was for a sexual purpose" and the way they had deceived Becky's father Darren Galsworthy and his wife, Matthews' mother, Anjie in the days that followed was "particularly cruel and unusual".

'Obviously dishonest'

As a missing person's inquiry began, the couple dismembered Becky's body in their bathroom and packaged it in cling film before hiding it in a nearby shed.

Matthews watched "borderline legal" pornography regularly, showing petite teenage girls, and the jury heard a video about the rape of a teenage girl was found on a laptop at their home.

Image caption Becky was suffocated at her home and her body was later moved and dismembered

The judge said both Matthews and Hoare had given "obviously dishonest" accounts of what happened to the jury - Matthews had claimed he was trying to scare Becky into changing her behaviour while Hoare said she knew nothing about any of it.

"The evidence proves, and I am sure, that Nathan Matthews had developed a fixation with having sex with petite teenage girls and Shauna Hoare had been persuaded to participate in this fixation," said the judge.

"It is difficult to understand how Mr Matthews and Ms Hoare thought that the kidnap would end."

Media playback is unsupported on your device Media caption Becky Watts' grandfather John Galsworthy: 'Time can never heal'

Texts between the two about kidnapping girls, uncovered by police, showed "how much their understanding of where proper boundaries of conduct began and ended had become corrupted and warped".

The judge said Matthews would be 61 before being considered for release "and the reality is, he might never be released".

Hoare was convicted of manslaughter because she had participated in a kidnap where any "sober and reasonable person" would have known some harm would come to Becky.

The judge appeared emotional as he paid tribute to Becky's family for the "dignified way in which they have conducted themselves throughout these proceedings". He said it was clear neither defendant had "truthfully" said what happened that day - and he understood the family's frustration about it.

Media playback is unsupported on your device Media caption Det Supt Mike Courtiour: "I hope these sentences will bring some comfort to the family"

Becky had lived with her father, Darren and Anjie since she was three. Anjie's son Matthews had grown up nearby with his grandmother but had a close relationship with his mother and the family.

In other impact statements read out in court before sentencing, Darren Galsworthy said: "We will never understand why this happened but we now believe we were just disposable pawns in a plot borne out of hatred, jealousy and greed. The heartless, cold and calculating perpetrators of this despicable act of evil can never be forgotten or forgiven."

"These family members sat in our home, knowing what they had done and watched my very public descent into madness and despair. They said nothing and carried on with the pretence of helping us and showed no emotion at all."