This is What Murderers Are Like?

While searching for stuff on parents murdering disabled children, I found a different case. Three eight year olds were murdered. When they asked a probation officer who he suspected, he named a bipolar 18 year old because 'he wore a black leather coat in all weather and listened to "devil music" such as Pink Floyd and Metallica.'
They questioned that boy and his developmentally disabled 17 year old friend, and the 17 year old confessed that he, the 18 year old and another friend had stabbed and raped the three boys. The problem: the victims had been beaten instead of stabbed (they had what appeared to be stab wounds, but were actually from wildlife), and had not been sexually assaulted.
Despite the evidence against their guilt, they were convicted. The 18 year old and 17 year old were convicted to life in prison, their friend to the death sentence (this was in US). Luckily, before the last sentence could be carried out, the case 'fell apart' and the three teens were declared innocent.
My question is: how much of this is related to the disabilities that at least two of the suspects had? I know of a bipolar man who was shot as a suspected terrorist, and it seems bipolar people often seem similar to the stereotype of a murderer. Was the fact that the one boy was bipolar related to this?

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