Port Arthur. The location is seared forever in the national consciousness.

35 dead. The scale of the killing shocked and horrified us all.

Martin Bryant. Australia’s worst mass murderer.

We know precisely where it happened. We know how many people died. We know that scores more were seriously injured, that so many families were shattered that day. And we know who was responsible.

What we don’t know is precisely what motivated Bryant to kill and kill again. Nor do we know how he accounted for his killing spree once he was arrested and charged. That is, until now.

Startling new video has emerged along with chilling first person accounts never before seen or heard that have enabled Sunday Night to build the most definitive picture of one of the nation’s darkest days.

Why so many victims? How did Bryant explain his actions? Was he chasing infamy? Was he contrite? Did he comprehend the magnitude of his crimes?

This Sunday Night major event features new, deeply personal and detailed accounts of Martin Bryant – the man and his motivations – from those who came to be closest to him in the days, weeks and months that followed the Port Arthur atrocity. They’re men who got inside the mind of a monster.

And what they found there was shocking, unbearably so.

We’ll also hear from the girlfriend who was showered with money and proposals by a simple, illiterate loner harbouring a terrifying murderous intent. And in never-before-seen video, hidden from the public and obtained by Sunday Night, we’ll see and hear arguably the most authoritative account of all.

Sunday Night’s Mike Willesee leads this powerful and important investigation as Australians continue to crave answers to the big questions still surrounding this appalling crime 20 years on.

This SUNDAY NIGHT Major Event hosted by Melissa Doyle airs on Sunday, March 6 at 8.30pm on Seven.