Long, lean and languid-limbed with Mick Jagger lips and hair to his shoulders, Richard Neville was the very picture of a bell-bottomed hippie. A pioneer of the war on deference, the one-time UNSW student newspaper editor was convicted and sentenced to prison for publishing a rude satirical magazine called OZ. That was 1964.

In 1966, aged 25, Neville upped stumps to London, went fluorescent and co-founded a psychedelic version of OZ. All too soon, he found himself at the centre of the longest obscenity trial in British legal history, charged with conspiring to corrupt public morals by publishing an offensive depiction of Rupert the Bear. The case was a sensation, a free speech milestone. John and Yoko protested the guilty verdict. Between court appearances and spliffs, Neville knocked out Playpower, a gleefully chaotic insiders’ guide to the counter-culture from the barricades of Paris to the Istanbul–Kathmandu trail. But the hash cookie had begun to crumble. All too soon, the hippy hippy shake was all shook out. Worse, there was a serpent in the garden.

Since 1970, Charles Sobhraj, a burglar, con man and smuggler, had been robbing satori-seeking Western stoners from Turkey to Thailand. The Paris-raised son of a Vietnamese mother and an Indian father started out by drugging and swindling his marks. Before long, he was killing them. Continually on the move, he eventually murdered at least 12 people.

In July 1977, commissioned to co-write a book on the serial killer, Richard Neville flew to Delhi, where Sobhraj was facing trial, arriving with a “crude theory of Charles as a child of colonialism revenging himself on the counter-culture”. Instead, he found himself being courted by a psychopath.

Over the next four months, Neville interviewed the charming, urbane and self-assured killer in a stifling courtroom cell. Eventually, on condition that Neville never testify against him, Sobhraj confessed to five known murders in Thailand and two in Nepal. He called them “the cleanings”.

Neville published the confessions in The Life and Crimes of Charles Sobhraj and eventually returned to Australia and a brief attempt at a television career. Sobhraj was sentenced to 20 years’ jail, broke out, duchessed the system and was deported to France a free man in 1997. Six years later, he was recognised in the street in Kathmandu and arrested in the casino of the Yak and Yeti hotel. He was sentenced to life imprisonment and there he remains, a privileged inmate.

Richard Neville describes himself as a practising futurist. Charles Sobhraj is on Facebook.