Toss the guards in that soup pot too. They may be less culpable than those who create the environment and enable the behavior, but they still participated in it. They still knew they were torturing someone. That (and even if) they didn’t mean to kill him doesn’t get them off the hook in the slightest, IMHO.
I get the reason for a shower like that, there are times when inmates are uncooperative, and you need to do something about hygiene, so putting them in there and rinsing them off for a bit may be the “best” method of dealing with uncooperative prisoners.
Using it as a form of punishment, however, is simply torture. Unless the sentence handed down by the courts and the jury says that the inmate should be subjected to cruel and unusual punishment (which even a PD should get appealed on constitutional grounds), then the guards are not there to punish. The guards deciding on their own that this inmate deserves some extrajudicial punishment should be considered a crime against humanity.
I am against torture entirely, but the small part of me that is for fairness over pragmatism is tempted to want to see these people who have abused their authority in order to degrade and dehumanize other human beings get the same treatment that they dished out.
It’s also stupid, prison riots don’t start because people don’t want to be in prison, prison riots start because of the conditions in the prison. You start torturing inmates, and your population can quickly become uncontrollable. And if one were an inmate subjected to the tortures from the guards, I think he would have little personal ethical reason to not return the favor.