Guys, there is a federal law that forbids those that are users of illegal drugs from possessing firearms. That is why that question asking if you use drugs is on the 4473.
I have actually seen it successfully prosecuted a couple of times.
I have also seen several federal cases based on...
That is the Georgia criminal code; however, it appears this is a federal investigation, so, assuming that they are prosecuted federally, some different rules, enhancements, and so on will apply.
EDIT: apparently some are being charged federally and some on the state level, so apply what I said...
This news report shows that Myers (dead kid) had gunshot residue on his hands. I guess the sandwich was a 9mm on rye?
http://www.foxnews.com/us/2014/10/15/tests-show-gunpowder-residue-on-teen-shot-by-off-duty-st-louis-cop/
This is interesting and not the first time that this has happened in this area. Although the last time, I believe it was an assistant to the coroner (although it was a different coroner).