In August a young man called Harry Dunn died when a car driving on the wrong side of the road crashed into his motorbike. The only suspect has left the country, and there’s nothing the police can do to get her to come back. Anne Sacoolas' husband works for the US government at RAF Croughton in Northamptonshire, and because of diplomatic immunity she currently cannot be prosecuted. The BBC’s Duncan Kennedy has interviewed Harry’s parents. And BBC diplomatic correspondent James Landale explains why diplomatic immunity exists in the first place.

Presenter: Matthew Price