How the damning material in videos about the treatment of young boys in the Northern Territory Don Dale Youth Detention Centre came into the hands of ABC Four Corners is not known but with a Royal Commission to investigate the system all may/will be revealed in due course.
The public record includes The NT Children's Commissioner Don Dale Youth Detention Centre Report to Minister September 2015 pdf that provides details of one of the worst instances of mistreatment but not the videos.
Almost certainly the video footage wasn't offered up by those responsible for the system or delivered on a plate via the Information Act 2002.
If someone on the inside thumbed through the Public Interest Disclosure Act beforehand he/she would know it provides protections for reporting through official channels but none for public disclosure to the media or anyone else for any reason, falling short of what is regarded as best practice.
A look further to the Northern Territory Criminal Code Act Schedule 1 Clause 76 would remind that unlawful communication of confidential information could get you three years in another detention centre.
And there is no available defence to a charge such as absence of harm or the importance of disclosure in the public interest:
Disclosure of official secrets
(1) Any person who, being employed in the public service or engaged to do any work for or render any service to the government of the Territory or any department or statutory body thereof, unlawfully communicates confidential information coming to his knowledge because of such position is guilty of an offence and is liable to imprisonment for 3 years.
(2) If he does so for purposes of gain he is liable to imprisonment for 5 years.
A provision in similar terms is S 70 of the Commonwealth Crimes Act.
Recommendations for repeal and reform first floated in 1991 reinforced in 2009, have been ignored by governments since.