This man is not a responsible gun owner or man who was defending his life (except at the very start). He acted out cold-blooded murder when the threat was already neutralized.
It is in the interest of gun rights and of basic human morality to condemn what he did. If what we know so far is true, he should never leave a cell again.
That said, innocent until proven guilty.
All of the information about what happened came right from the shooter/homeowner. If we are to believe everything he said, then we must believe that, as he stated, he had been burglarized from 8 to 10 times in the past. In that light, it would have been illogical for him to not eliminate the continuing threat of being burglarized an indefinite number of times in the future.
Aside from that, for you folks who have a bible based moral system, I do believe that it says something about if a thief digs under the wall of your house, it is not murder if you strike him dead. It does not say you have to stop shooting (or striking), him if the threat is incapacitated. Law is law, not morality.