Since then, he became entwined with Sobhraj's life, a bond of hate that persists even today, years after his retirement and moving from Bangkok to New Zealand.

The Dutch diplomat's story forms the basis of a book on Charles Sobhraj's crimes, including alleged serial murder of western tourists, a docu-drama and media reports.

Knippenberg also wrote an article for Reader's Digest, slamming Sobhraj as a serial killer and highlighting his role in exposing Sobhraj - an article that was presented in Nepal's court by lawyers who hailed it as proof that Sobhraj killed an American tourist in Kathmandu in 1975.

Last year, Coutant-Peyre successfully fought a battle against a website hosted from Knippenberg's home country that sought to portray Sobhraj as a convicted killer acknowledged to be so by the UN.

Sobhraj says he has never been convicted for murder by any court and labelling him serial killer amounts to defamation. He also says that the Nepal court was the first to sentence him for murder five years ago.

However, since that case is still being fought in Nepal's Supreme Court, the issue remains sub judice.

Last year, Coutant-Peyre flew down to Nepal to present to the UN the Dutch website, believed to have been hosted by Knippenberg, whom Sobhraj accuses of being involved in a vendetta against him.

On the UN's intervention, the Dutch authorities closed down the website.