The gun had the serial number filed off (or removed) - illegally obtained and possessed. If they want to get rid of guns all together, then they might as well disarm police, DHS, TSA, FBI, the DoD and all of them.
Professor, I have a thought for you:
Americans have owned weapons for hundreds of years yet we never saw this type of violence before with the exception of war where it was necessary. In fact it gave us this great nation you now live in. Now we see a new type of violence which is more brutal and vengeful during a time when socialist policies are being taught in our schools and the government has embraced it. Do you see the correlation? Socialism = more death by guns. Guns were already here. See how I made that same leap of faith like you did? Sorry, forgot “leap of faith” is a religious term which you despise...