Oamaru's Wayne Stringer was New Zealand's "Nazi Hunter".
In 1992 he spent a year investigating 47 "displaced persons" suspected of involvement in Nazi war crimes, who came to New Zealand to escape prosecution at the end of World War II.
His year-long investigation is the focus of Inside New Zealand's latest documentary, Nazi Hunter, screening on TV 3 tonight at 9.30pm.
It all began in the early 1990s when the Jewish organisation the Simon Wiesenthal Centre sent the New Zealand Government a list with 47 names of "displaced persons" who were given a home in New Zealand. All were said to be suspected war criminals associated with mass murder and genocide.
The list was one of many sent to other countries around the world, and signalled the beginning of the investigation.
Mr Stringer, who was in charge of the CIB in Blenheim at the time, applied for the job to become New Zealand's "Nazi Hunter".
It took him around the world - from Australia and Canada to the Baltic States, where he was given access to war records held for years in KGB archives, and visited the killing grounds in Lithuania and Belarus.
He quickly narrowed down the list, interviewing every person who was still alive in New Zealand, though many of the suspects had died and some names were cases of mistaken identity.
"It was fascinating and some of them were completely innocent," he said.
"I remember one chap who was a lieutenant in the Latvian SS. The Germans conscripted every Latvian over the age of 16 and sent them to the Russian front, tattooed them so they coundn't go backwards because the Germans would kill them, and they couldn't go forwards.
"He married a Jewish girl, they were a lovely couple so it was a pleasure to tell them that they had been discounted completely."
Mr Stringer found it difficult to dismiss others so easily.
It was always going to be difficult to prove any of the suspects guilty, more than 50 years after the crimes.
Knowing that probable war criminals had lived and died in New Zealand without answering for those crimes strill frustrates Mr Stringer.
"It took a year out of my life and it was hard knowing that there wasn't going to be a prosecution," he said.
"You had the horrible old men and there was just something about them."
For Mr Stringer, the investigation changed his life and, when it was revisited last year for the filming of the documentary, the memories came flooding back.
After years of major inquiries and homicides for the New Zealand Police, and heading the Oamaru police for about eight years, Mr Stringer is quite happy in his latest role - working for Age Concern in Oamaru.