Nonsense. You can't prove that statement.
TMK at present, we have no idea whose gun it was or how he obtained it. He may have bought it illegally on the street.
You haven't even specified what sort of gun control you want to see, that you think might have made a difference here. How can we take your assertions seriously when they are so vague?
You assert "those who want to obtain guns will be able to do so anyway" two sentences later.... this is actually the more correct statement, as we have no evidence that gun control laws actually reduce violent crime or keep criminals from arming themselves, or keep irresponsible people from being armed. They simply turn to the black market if they can't obtain guns via legal channels.
We've already successfully put to bed the idea that any gun control legislation then under consideration, nor any proposed afterward, would have had any significant likelihood of stopping Sandy Hook. I see nothing in your posts to indicate what would have stopped this shooting.