***spoilers ahead***
What motivated Donny to kill the pediatrician? Was Donny himself a victim of abuse at one point in his life? What condition did he suffer from?... seemed like he had a mild case of Aspergers... Was this a result of abuse he suffered from as a child, perhaps?
At the end, did he call the cops himself?
"Tyler was silent because that man took something away from him, he was a shell of of boy" as evidenced by the car mechanic also being the shell of a man and by Donnie being the same way. Yes I believe he was abused, maybe not by the doctor but perhaps by doctor's father...the doctor stated "This office belonged to my father and his father, I would hate to loose it now". I believe Donnie did call the cops and the sheriff already knew there was evidence against the doctor and him, he couldn't hide it this time because the evidence was out of his jurisdiction. I would think that most juries would tend to go soft on facts and evidence like this.
shareI think he was abused as a child .
That would explain his obsession and motivation.
His mother was a bible freak and his dad died of drink.
Classic dysfunctional family setup there
Not sure who called the cops at the end