A feeling of disengagement from society is, of course, not a good environment to grow up in. But that in no way excuses excuses such evil acts, nor does it explain them because it is not enough, as again I would point to the large number of people in the same situation who do NOT commit such acts as proof of this. There is something wrong with the people involved, and that was NOT done to them by society.
Furthermore, whilst there are genuine economic and political issues, many of those who think that they have no stake in society are simply wrong, and are bent that way by their selfish attitude that gives them a false sense of entitlement. The same sense that makes them want to go out and loot a tv.
By far, the primary issue here is personal responsibility. It must not be ignored as a factor.