General Discussion
In reply to the discussion: Tennessee father and son dead after AR-15 goes off and ammunition-filled room explodes [View all]web search turned up these sites, but there is much more information available on the "pipeline" which supplies lethal weapons to both Chicago and New York (among other cities).
http://www.nydailynews.com/new-york/new-york-tough-gun-laws-weakened-states-article-1.1431333
http://blog.timesunion.com/guns/the-iron-pipeline-of-illegal-guns/2295/
http://www.wbir.com/news/article/201957/2/TN-gun-laws-or-lack-thereof-under-attack
This is nothing new, and states with lax gun laws have been a source for black market guns for years. This is the major reason that MAIG was formed, and other gun control organizations are joining in the fight against the practice.
Edit: One more link for Chicago:
http://www.chicagomag.com/Chicago-Magazine/The-312/January-2013/Chicago-Gets-Its-Guns-Where-It-Used-to-Get-Its-Blues/