An investigation carried out by the lawyer of a young American charged over two car crash deaths cast so much doubt on the police investigation the case was tossed out of court.

It also means family of the young men killed - Yvarn Manaia Tepania, 24, and James Alexander Hamiora, 26 - may never have the answers to a crash which has come to haunt their lives.

Reiss Berger, 22, was facing charges for multiple driving offences - including two charges of aggravated careless driving causing death - after the crash south of Kerikeri in April last year.

Berger had