The New Zealand man who murdered British backpacker Grace Millane committed violent sex crimes against at least two other women, a court revealed Tuesday, as police urged any more victims to come forward.

The Supreme Court overturned orders banning Jesse Shane Kempson being identified as the predator who strangled Millane in December 2018 after the pair met through the online dating app Tinder.

The murder shocked New Zealand, which is usually regarded as a safe place to travel, prompting a tearful apology to Millane's family from Prime Minister Jacinda Ardern after the young traveller's body was found.

The suppression orders on reporting Kempson's name remained in place even after his murder conviction in November last year, with the court offering no explanation at the time for the highly unusual move.

But a judgement released Tuesday revealed that he was still facing two trials for sexual offences when the Millane verdict came in, and the court feared naming him could prejudice those proceedings.

In the first, he was convicted of sexual violation, assault and threatening to kill his former partner, reportedly brandishing a knife to her throat.

The second resulted in a rape conviction involving another woman that Kempson met on Tinder.

He was sentenced to a total of 11 years for the sex crimes, to be served concurrently alongside the sentence of life with a 17-year non-parole period for Millane's murder.

The killer of Grace Millane, whose murder shocked New Zealand, has been named publicly for the first time
The killer of Grace Millane, whose murder shocked New Zealand, has been named publicly for the first time AFP / Marty MELVILLE

Detective inspector Scott Beard said the "callous, narcissistic" serial sex offender may have more victims.

"There could well be other women out there who Grace's killer may have offended against," he told TVNZ.

"If they're not sure what to do, come to the police and speak to us."

Kempson's appeal against the Millane murder verdict was rejected last week and the court found there was no longer any need to stop the 28-year-old being named.

Millane disappeared on the eve of her 22nd birthday, within days of arriving in Auckland while on a year-long, round-the-world trip after graduating from university.

She met her killer for the first time on the evening of her death after matching with him on Tinder and the pair went back to his city-centre apartment after visiting several bars.

Kempson's lawyers claimed at his trial that she accidentally choked during a sex game gone wrong, a defence rejected by the jury, which unanimously found him guilty.

The case prompted British lawmakers in July to ban the so-called "rough sex defence" in sexual violence cases, with women's advocates pushing for similar reforms in New Zealand.

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