The video at end shows the whole incident, including the shooting obviously. So be warned.
I think I am torn. I think going back and shooting the helpless kid was wrong. I mean the Pharmacist comes back into store, walks right by kid, turns his back to kid, goes and gets another gun, hurries back and then shoots kid 5 more times while kid is down and obviously wounded (originally shot in head). If he still felt threat then why turn your back to kid?
The original shooting was obviously, IMO, ok. But the threat was over. Does walking past kid and going and grabbing another gun make this premediated and thereby First Degree Murder? What I learned in law school says yes. But should we take anything else into account (stress, anxiety of having gun pointed at him, etc.).