I'd say it is/was poor training and apathy.

Probably before your time but you should look at the Carmen Laurence \ Penny Easton suicide in 1992. I was told that all Commonwealth funding of family court legal aid lawyers was terminated in order to fund Laurence's defense council in charges of causing the suicide. I suggest that it also resulted in the suicide of quite a number of Family Court litigants who were left at short notice with no legal representation. I was one.
The PTSD resulting from the illegal treatment by the court judge & his judgement, the prosecuting barrister & lawyer left 3 judges at appeal hearing claiming that as Australia had not incorporated internationally agreed to human rights covenants into Australian law there was no requirement for them to uphold those laws. However they pretended to make orders to protect my daughter - they didn't work either.The PTSD has never been treated.

For many years I've pointed out that many Australian government's legislation effectively results in senicide. Like my remarks on Ukraine & now Gaza they have been ignored.

Ask an Aussie lawyer.

At the very least it is negligent homicide and reckless disregard of life.
The Stanford Prison Experiment is the cautionary tale that all prisons/institutions and those who manage them should be aware of. That experiment forewarned the potential dangers so,...there is no excuse and no defense.

It's pretty obvious what happened. The prison staff doesn't value the lives of their young inmates, something that is also common in the US. The fact that he is black, probably made his life even less valued. And finally, the staff had probably become tired of his repeated suicide threats, so, in a nutshell, they decided to stop caring and just let it happen, since it seemed inevitable anyway, in their eyes. And reckless disregard for life, should be 2nd Degree Murder, same as it was with the cop that killed George Floyd..

We humans are failing at decency and empathy.