So you mean, that certain childhood/life conditions and experiences shape our personalities and behaviour? Yes I totally agree with that.
Like a starving African child soldier killed someone, because of his conditions. So was he evil? Personally, I think "no" more than "yes": not all actions are evil, some can be "justified" depending on the circumstances, except things like Rape/Child Molestation etc.
So, although the act of killing someone at random is evil in my opinion, the circumstances make me think that the boy would not neccessarily be evil, but a victim of poor, war torn upbringing. The real evil person(s) would be those who destablize, sell weapons, and constantly prevent recovery of the area.
Life has too many conditions, circumstances, and opinions in order for us to truely objectivify "Good" and "Evil". That's my opinion, however I do believe Humans universally can agree on certain "Good/Evil" things, i.e we all agree Rape/Child Molestation is bad.