As we record this episode, the Victorian High Country is the scene of an intense hunt for a man accused of shooting and killing two police officers, and injuring a third.

The man Victoria Police say they are searching for is Desmond Christopher Filby, aka Dezi Freeman, a radicalised conspiracy theorist, and self-described “sovereign citizen”, who espoused hatred for police.

But what is a sovereign citizen, and how widespread is the movement in Australia?

We bring you this episode earlier than usual, with associate professor Dr Joshua Roose, who was an expert witness in a similar, notorious shooting in Queensland, on whether the sovereign citizen movement has been underestimated