Indigenous Affairs Minister Nigel Scullion admits "heinous" treatment of teenagers in NT detention had not piqued his interest before airing on national television.
He insists he wishes he knew earlier of allegations of teens being stripped naked, tear-gassed and held in solitary confinement at a youth detention centre in 2014 and 2015.
"You don't know what you don't know," he told reporters in Canberra on Tuesday.
"It hadn't come to my attention, hadn't piqued my interest, well, sufficiently.
"I'm not making excuses about it, I would have loved to have known earlier."
The Koori Mail published an article last September airing allegations boys at the Don Dale centre had been gassed - as shown in the ABC footage.
Senator Scullion admits hearing some media reports last year about Don Dale but says he assumed the NT government was dealing with it.
"It was all about `this has all been taken care of'," he said.
However, despite early promotion of the ABC's Four Corners program, Senator Scullion didn't watch the footage until he received an "agitated" phone call from the prime minister.
He was instructed on Monday evening by Malcolm Turnbull to "go home and see it".
Senator Scullion says what he saw shocked him to the core.
"It was some of the most disturbing footage I have ever seen," he said.
"We have a system that if you are going to harm yourself the most helpful thing is to tie you down and put a bag over your head - if that is world's best practice then I am just stunned."
About 85 per cent of NT prisoners are indigenous and almost half the nation's youth detainees are Aboriginal or Torres Strait Islanders.
Senator Scullion believes centres like Don Dale are part of the problem not the solution.
Officers at the centre had no concern that their "evil" actions were captured on camera because they knew there was no chance of it ever coming to light, he said.
But the minister believes that culture of cover-up exists within correctional services, not within government, and wants to see guards behind the cruelty punished to the full extent of the law.
"Imagine having five blokes, three of them rush in and smash a tiny child against a wall," he said.
"I don't think those people can be repaired and if they can't be repaired they can't be in the system."
Mr Turnbull immediately launched a royal commission into juvenile justice, with evidence expected to begin in September.
It's understood Senator Scullion was aware of the Four Corners program before it aired.
The minister insists Mr Turnbull's agitation during the Monday night phone call was not directed at him, but because of the prime minister's distress about what he had seen.
Labor senator-elect for the NT and indigenous woman Malarndirri McCarthy said Senator Scullion had made some "very strange comments" about being out to dinner while the Four Corners program aired.
"I am aghast really," she told ABC radio on Tuesday.
"I think it's a real sad and shocking indictment of the numbness that people feel that this is not being taken seriously."
