Of course they do. This "criminals don't care about the laws bullshit" is just that, bullshit. If the one selling or giving someone a gun knew they could go to prison for doing so they would think a lot harder about doing it. And if the criminal knew he could reduce his sentence by giving up that individual he would do it. To say it would not make a difference because a criminal is a criminal is simply fucking stupid.
Bullshit. If I sell a gun to someone who later uses it to commit a crime I am not liable for jack shit. If it were a felony to sell a gun to ANYONE, criminal or otherwise, the number of illegal transfers of ownership would drop drastically.