'Do you really think that finding out what excuse someone gives to their behaviour will prevent it happening again?'
One of the abusers gave an excuse
"When asked by Judge Richard McNamara for a more definitive motive , Waldron seemed at a loss.
‘Punishment,’ he said, shrugging his shoulders."
but the prosecutors did not accept it or believ that that is why the abusers acted in the way they did
"prosecutors said they believe it had something to do with the victim, who is mentally challenged, no longer receiving financial assistance from the government because he wasn't enrolled in school at the time"
"I fail to see how giving an excuse for their behaviour helps the victim"
Prosecutors do not accept excuses, they look for reasons why and motives. That is totally different from an excuse, because there is no excuse, but there is a reason why.
I believe that understanding how it can happen that someone can do things like that will help stop those things happening in the future, and that is why criminologists and psychologists and psychtatrists try to understand how these things can happen.