I agree with your reaction to the crime Lookout but there is always cause and effect imo. If these children became so evil there has to be a reason, although I am not trying to excuse the crime. They were either born that way or they were taught to behave that way. Children learn by example imo. 
As we all know,a child learns " right from wrong " at a very early age. I agree that children learn by example,but not all of them do, either because of an inborn rebellious nature or a mental health issue.
Many children from bad backgrounds do well in life because of their aim and determination to get themselves out of a bad family situation, as they look to the future. Granted,this was more a time when job prospects were more of a guarantee than now but no teen " in their right mind " would have resorted to murder when things were tough.
I can't bring myself to excuse the monstrous behaviour of these teens and the excuse of a bad family background doesn't do it for me at all. Not when I've known of horrendous family situations in the past where neglected children had to deal with alcoholic parents.I've seen it all Maggie and heartbreaking as it was,those children had no thoughts of crime in any way,just to do well at school and get a job as far away from that household as they could.
This is why my reasoning is so diverse and controversial.