For Arno Arr Michaelis, anti-social behaviour became a kind of addiction as a kid.

“Hate was just another part of the thrill,” he says.

“Really what I craved was to repulse civil society and nothing appals people more than a swastika.”

He joined a neo-Nazi skinhead group in the US for seven years and was part of the worldwide Hammerskin Nation movement.

By 1994, Mr Michaelis was a single parent to his young daughter in Wisconsin. He decided to leave the group after a friend was shot dead in a street fight and others were jailed …