There are further calls for DNA testing to be mandatory after it finally solved a 20-year-old Christchurch rape case.

The Sensible Sentencing Trust is supporting a Christchurch Judge's call for a preventive detention report to keep a rapist behind bars.

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Yesterday Devon Charles Bond pleaded guilty to six charges, including two of sexual violation, rape and abduction dating back to 1994.

He entered a woman's home, shut off the power and threatened her with a knife, before tying her up and raping her.

He wasn't found until a DNA match in 2014.

Justice Gendall yesterday urged the Crown to prepare a preventive detention report.

Sensible Sentencing Trust spokesman Garth McVicar said DNA is crucial evidence.

"Everybody who is convicted of an offence should give a DNA sample, compulsory. More samples that are tested the more hits we're getting. So we've got changes happening here, not fast enough."

Mr McVicar said Bond should never be freed.

"Preventive detention is really the only sentence that can protect the public. He may never be released and realistically we've got to ask the question why would you ever release an evil-doer like this."