Exclusively on 60 MINUTES, Tara Brown reveals how Police investigated Australia's most evil family and found the murderer of schoolgirl Tiahleigh Palmer; plus the most spectacular film set in the world, 11 kilometres under the sea.

A young mother trying to protect herself and children from a violent partner picks up a knife. The attacker lunges and the knife pierces his chest by a tiny 14mm. He dies and she's charged with murder. Tara Brown investigates a tragedy.