Now, try asking in a debate the proportion of crimes committed with legal weapons vs illegal weapons and watch your opponent start dancing around the question! Good luck getting a straight answer.
Even at that point, "legally obtained" still included borrowing one from a friend or family member.
That's interesting! Why would they hide such stats?
The pro-2A response to gun control requests based on crime is often to say "don't ban my guns - just make 'felon in possession of a gun' a life-without-parole offense".
Citation needed here. Especially in the south.
Most of them come from purchases at gun shows (as laws are considerably laxer on private sales). The serial numbers are filed off, then they're hidden in abandoned buildings by a person who rents the guns out to be used in murders. The same illegal guns are typically used in numerous murders, making it more difficult to trace them back to any particular person, if they are found.