Nathan Matthews has been jailed for a minimum of 33 years for murdering his stepsister Becky Watts, 16, in a sexually-motivated kidnap plot.
His girlfriend Shauna Hoare, 21, has been sentenced to 17 years for manslaughter.
At Bristol Crown Court, Judge Mr Justice Dingemans said he was sure on the evidence "that the planned kidnap of Becky was for a sexual purpose".
Matthews suffocated his stepsister at her home in Bristol on 19 February.
The judge appeared emotional as he paid tribute to Becky's family at the end of sentencing.
Judge Dingemans told Hoare she had been 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.
He said the case was of a "particularly high" seriousness "because of the planning of the abduction for a sexual purpose, the taking of the implements described and a weapon (albeit non lethal) and the murder of Becky".
He added: "In my judgment the behaviour of both Nathan Matthews and Shauna Hoare in feigning concern with the family, as the family desperately searched for Becky, is a further, and serious, aggravating feature.
"In my judgement the appropriate sentence for Mr Matthews is a mandatory life sentence, with a minimum term of 33 years. This means that 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."
http://www.bbc.co.uk/news/uk-england-34812317