Thats a very good question. One I have been thinking about myself. Why was someone taking pictures in the first place? I would assume they knew something was going on and they did not feel comfortable going to their superiors with the info... and why was that????
My husband and I discussed this very point.
To use the analogy we finally settled on:
Your mother is a cop. She gets beaten up really badly by a gang member one day. A few weeks later, she arrests that gang member.
Your father is a guard at a prison. He gets his hands on that gang member and beats the living snot out of him for what the gang member did to your mother.
Do you turn in your father?
Now, to turn that analogy over to the situation at hand.
Soldiers are supposedly like family (I don't know, I'm not in the army or anything).
You have this prisoner who was trying to kill your brothers/sisters (or yourself). Maybe he did kill someone you knew. Then you get access to him. And you get your revenge.
Will your other brothers turn you in for enacting your revenge?
In an ideal world, yes, to both those questions. You would turn in your father/brother and not only would they not be upset with you, they'd thank you for doing the right thing.
However, we don't live in such a world, and I don't know about you, but it's a real thought provoking question over whether or not I'd turn in my family for doing something wrong if it was so "justified" in this manner.
I suppose that says something bad about me. I think what was done was terrible and should never have happened, but I can now understand WHY it went unreported, and while I would like to say that if I was there and saw it happening, I'd do something to stop it. But thinking about it now.. would I turn in my father for beating up someone who hurt my mother? It isn't as cut and dried as if my father went insane and started to beat up some random person or killed someone. In that case, I'd be really really upset by the fact that I'd have to turn in my dad, but I'd do it.
So, my guess is that the soldiers who were doing it were doing it because these were people who were trying to kill them.
And the soldiers who saw it happening but didn't report it, didn't report it because you're over there, with people you consider "family", and are you going to turn them in? And have them mad at you, peer pressure on you, and the like. What happens if someone did turn them in and the person in charge didn't care, or was involved? Do you go over the head of your superior?
So.. in my bad way of summing things up, there are lots of reasons why it wasn't reported, which range from "family", to "peer pressure" to "tried and failed".