Actually I do...
From what I gather, Hitch is proposing that morality originated from the evolutionary development of social groups (something that anthropologists have proposed). Specifically, members adopted the morals of the group they identified with...which were largely based upon survival of the group. These morals came into existence in parallel with the group's existence.
So obviously, this idea is more about how morality came into being...not necessarily how it's developed today. However, let's apply this idea to your example...
These hoodlums probably identified with their gang as their primary social group....and any other groups they identified with were secondary (or further) to this primary group. The morals of this group are based around survival of the group...and as a criminal group, things like theft, murder, etc are part of that morality.
As I said, this conflicts with the morals of the larger group they are a part of (whether they recognize it or not) citizens of the United States. The morals of that group are so vehemently opposed to murder....we've created laws against it. When this gang violated those laws, they created a conflict, a schism between the two groups they belong to and it's being resolved (in court).
I understand that a lot of this might be over your head, so just ask yourself...how many here on C.F. probably consider themselves christians first and U.S. citizens second? How many would consider their christian morals over their national morals? How many would (for example) deny a homosexual couple a marriage license or make abortions illegal if they could?