Dean Stewart Cameron began a life sentence yesterday for the rape and murder of schoolgirl Marie Davis, but the Crown says it will seek preventive detention because he has raped before.

Justice Lester Chisholm sentenced the 39-year-old road worker to life after the jury returned guilty verdicts in the High Court at Christchurch.

But Crown prosecutor Chris Lange asked for the open-ended preventive detention sentence to be considered, and Justice Chisholm remanded Cameron to August 24 for the necessary reports to be prepared.

In 2004, Cameron was jailed for four years for rape after pleading guilty at a retrial. The verdict had been annulled after the first trial. At the time Judge Stephen Erber said Cameron had unnecessarily put his victim through the ordeal of giving her evidence a second time at the second trial, before changing his plea.

In the latest case, Cameron denied raping and murdering Marie Davis, 15, from Papanui, but did not give evidence in his defence.

His defence team raised the possibility that the girl had gone to an early morning sexual encounter on the banks of the Waimakariri but later fell or jumped into the river, where her naked body was discovered 11 days later. The Crown's scientific evidence showed Cameron's blood was in the house where she disappeared, and his DNA was in semen found on her body.

"He didn't have a defence," the family of the dead girl said outside the court. Her mother, Janet Davis, said: "She was a beautiful daughter and we loved her so much." She was relieved that the right verdicts had been reached and at least Cameron was getting the sentence he deserved, but "it will never bring Marie back".