Keep in mind that I say the following as a supporter of the right to bear arms.
Since as far as I am aware, no existing gun law was broken before he went on his shooting spree. Nor were such laws broken in the case of Newtown. So bringing out the canard that we need to enforce the existing laws before even daring to consider anything else is really really not helpful. Now if you actually have something to say that pertains to this particular incident, please do so. However, the enforce meme exists only to delay doing anything, and not just with gun issues. So unless you have something relevant to say, either shut up or go on Fox News.
It is illegal for mentally-ill individuals to purchase firearms. This individual is clearly mentally ill. Therefore, we are not enforcing the laws we have on the books, and this is basically Jared Loughner Part II, though, we do not have a failed military psyche evaluation on Rodgers record.
When did this happen?
Not sure when it was made law, but Fed Law declares that any person who "has been adjudicated as a mental defective or has been committed to any mental institution" cannot own a gun. However being in therapy and even having serious mental illness is not the same as "adjudicated as a mental defective"...that requires a court.
So to the point, it is not illegal for the mentally ill to purchase firearms, only for those so mentally ill they have been committed or a court has deemed them mentally ill...and there is a HUUUUGE difference. And even with that, background checks often do not catch even those who are legally banned from owning guns. ...case in point...
http://www.cnn.com/2013/01/30/health/mental-illness-guns/And of course any effort to make tighter restrictions on the definition of mentally ill or the robustness of background checks would be destroyed by the NRA as an attack on the 2nd Ammend and freedom and democracy and America and how dare you for even thinking of it, go back to Russia