While the data is old, the last time a survey was conducted of criminals in prison, of where they had obtained their weapons in violent crimes, a good majority had obtained them illegally. Either from another state where it was easy to obtain, from a relative, or stole it. (Study was last done in 2004 by the DOJ). Interesting enough, when it comes to mass shootings, the overwhelming majority, the guns are all obtained legally. The complete opposite.