A man who was later found to be one of New Zealand's most notorious sex offenders could have been stopped at least two years earlier but the SIS failed to tell the police they had photographic evidence of his crimes.
Ronald Van Der Plaat kept his daughter as a sex slave for 23 years before she escaped his home in 1992.
But the SIS had him under surveillance and had captured photographic evidence of his crimes in late 1989 and early 1990.
They did not go to the police with their evidence meaning she was subject to horrific abuse for at least two more years.
The story has been uncovered by Investigative Journalist Guyon Espiner.
He speaks to Corin Dann.