I think Lott is opinionated, inflammatory, and important. I suspect he is probably wrong in his concealed carry conclusions. However in a complex matter like this, as in pretty much any scientific inquiry, those of us who are not specialists should rely on the consensus of the experts. In this case, there is no consensus on how concealed carry affects murder rates, so holding a strong opinion is unjustified. (It follows that we can expect a lot of ideological shouting.)
One thing that is known to raise murder rates is high and sustained unemployment. Neither concealed carry laws nor unemployment rates appear relevant to this shooting, however.