Well I certainly hope any shooter criminal or not would know that, when I mean "what a gun is all about" I am referring more to what they can be used for. A lot of people grow up with the idea that all guns are bad and all they do is cause blood in the streets. We need to teach them that in the hands of the right people they can save lives, and even be fun.
I am sure many do or did think guns were fun and knew guns could save lives. After all, there have been numerous killers who were military trained and several who enjoyed recreational shooting. Heck Klebold and Harris enjoyed going out an plinking.
Just because they know information does not mean that they assign the same values to the information.