Some emotional problems!!!!! You have to be a total psychopathic, narcissistic monster to do what you claim he did. Trouble is he has never shown any signs of these disorders in any other situation. 
1) people are good at hiding things though we know he was narcissistic enough to steal from his family.
2) the exact level of deparvity necessary is hard to calculate since it varies so much case to case/ is hard to quatify.
we don't know what other things he might have done that we are unaware of. Maybe he did have a personality he wasn't popular in school and didn't seem to have many friends.
Julie said he was constantly moaning about his hard work on the far and jealous anytime the fmaily spent money on others including his own sister who he was jealous of because she got a free ride while he had to work. He was jealous that his sister with mental problems who could not even be taught how to drive got a free place to live without having to work. He should have been thanking his lucky stars he was not like her. I don't get jealous if my parents help a sibling or even nieces and nephews out when they need it. He clearly had issues and some might have stemmed from being adopted, some from being dumped in a boarding school but there was more to it than that to be jealous of them supporting a sister with problems that prevented her from leading a normal life. That kind of jealousy is not normal at all. In fact it reminds me of the same kind of jealousy killer Ronald DeFeo Jr had where he felt his father should have given him the same amount of money to use for partying that he had spend on younger brother Marc's medical treatment (he had a broken leg from playing football).