The lead investigator in the Grace Millane murder case is questioning the use of "rough sex" as a defence

Millane's killer has been sentenced to life imprisonment with a non-parole period of 17 years at Auckland's High Court today.

It's almost three months to the day since the 28-year-old was found guilty of strangling the British backpacker in his apartment, on the eve of her 22nd birthday.

Detective Inspector Scott Beard says he's by by no means criticising the defence... but in his opinion it's a cop out...and re-victimises the victim.

He says strangling someone for five to ten minutes is not rough sex...it's murder.