The criminals steal their guns out of the homes of lawful Americans, or buy them from drug dealers who illegally brought them in with their drugs. Very few criminals, other than the insane, are linked to legal gun purchases and that is a fact. Legally purchased guns could be traced back to the criminal who purchased them, even those arranged through the Internet, therefore criminals do not legally purchase firearms. Its a chapter in Crime for Dummies and taught in Crime 101 in prisons. Gun Control freaks would have you believe different but they are wrong.
One of the reasons the Obama Admin claim of Mexican Drug Cartels bringing in guns from the USA is so stupid is why would they go to the expense and higher risk of capture by US police when they can bring in full automatic weapons of greater power from where they buy their drugs.
Central and South America is rife with cheap soviet weapons, such as DSHK's, RPK's and RPG's, and getting them is as easy as buying them from some governments, such as Venezuela, Cuba, Ecuador, and Bolivia. They just bring them into Mexico with their drug shipments. Why go to the high cost and high risk of bringing them in through the USA?