Changing parole laws could punish people who would otherwise lead successful lives, according to a parole specialist. 

The issue has been brought up following convicted murderer Paul Tainui killing again, seven years after being released on parole.

The double killer savagely raped and murdered a young Christchurch woman last year in a chillingly similar way to how he killed an ex-girlfriend 24 years earlier.

The 55-year-old's been sentenced to life imprisonment, with a minimum non-parole period of 28 years.

Lawyer Parole specialist Judith Fyfe told Mike Hosking the law needs to work for the many, not the few.

"You keep one person in there, you make a law for one person and it affects hundreds of people who would do quite well and be successful if they were released. This is the difficulty in managing the extreme.

"There are lots of people who have had life sentences and left prison to live very successful and productive lives."

The current Parole Act only allows prisoners to be monitored for one year.