Good story, but it's important to point out that there are no "former" Marines. They may get older, fatter and softer, but once a Marine always a Marine.
9mm kills perp carrying a .45. Yes, shot placement counts. And the man who successfully defended himself and family was carrying while walking his dog. That makes at least two imortant lessons to take away from this event.
Two, 9mm does not do well through barriers.
How did you come to this conclusion based upon the information in the article?
He didn't. That is one of the "two arguments often given," not a conclusion to be drawn from this shooting. He even numbered them for easy reading comprehension.