OKay, please don't flame me for this, I am only thinking out loud, and i don't mean to turn this into a racial issue, so please hear me out.
Ross is obviously a well educated man. I can see that in the way he talks and the way that he conducts himself ( no ghetto speak, very articulate, very good at putting his thoughts into logical order). He obviously has money, although at this point, I don't know how much is true wealth and how much is the appearance of wealth.
Regardless, there are a lot of people in this country that are intimidated by a young black man with money. The cockiness and attitude may be something that Ross has had to put off his whole life simply to combat what simple minded cretins are prone to saying and thinking about people like Ross. Once you have cultivated that as a defense mechanism, it's hard to just turn it off.
I just don't know. I'm not seeing foster dad as an outright murderer. The type to cover up a mistake, no matter how grievous, that is a possibility, but I just don't see killer on him.