for this to be of any use other than taking protection away from law abiding citizens (who's gun ownership has no impact on gun-crimes) you'd actually have to have a significant part of the population who have no problem committing murder but draw the line at owning a gun illegally, because that would be wrong.
Where do criminals get their guns?
They steal them off people who own them legally.
They get people who can buy a gun to make a straw purchase for them.
They buy them off legal gun owners at gun fairs and from classified ads.
They buy them from gun shops before they turn to crime, or before they get caught
In short, the route guns take to get to criminals is
Importer/manufacturer - dealer - criminal
or
Importer/manufacturer - dealer - legal owner - criminal
the supply of guns to criminals is dependent on the legal market for guns, restrictions on that restrict the supply of guns to criminals.
What astonishes me most about this thread is that there's an American who's been locked up for nearly 3 years without trial, because the administration says he's a terrorist.
No outcry.
There's a list of people not allowed to travel by air, because they are suspected of terrorism.
No outcry.
The same people are not allowed to by a gun.
Outcry.
Take away all their freedoms, lock them up, no problem, just don't try to stop them buying a gun.