Precisely what kind of gun control would have stopped Lanza?

From Reason:

... Lanza took the two handguns and the rifle that he had with him on Friday from his mother, who acquired them legally (and who was his first victim), the relevance of lies by gun permit applicants escapes me. Furthermore, the rifle, a .223-caliber Bushmaster M4 carbine, was not covered by the federal "assault weapon" ban (which expired in 2004) or by a smiliar law in Connecticut. Even if it were, plenty of guns equally lethal against schoolchildren (hundreds of millions, in fact) are widely available. That is hardly surprising, since the "assault weapon" category is arbitrary, based more on scary, military-style looks than features that make guns more deadly in the hands of criminals. Likewise, Lanza reportedly used "high-capacity magazines" (holding more than 10 rounds), but millions of these are already in circulation, and they can be readily fabricated no matter their legal status. (That's leaving aside the question of whether the need to swiitch magazines or weapons makes much of a difference in a murderous assault on defenseless people.) The notion that restrictions like these can have a noticeable impact, let alone that they can "end" or "stop" occasional outbursts of senseless violence, is hard to credit unless you believe what Obama insists he does not: that evil can be legislated out of the world by acts of Congress.

Outlawing high capacity magazines sure is a great idea. It would have allowed the little kids and their unarmed kindergarten teacher an opportunity to jump and subdue the gunman during the extra two or three seconds he would have spent reloading the smaller clips.

You can't legislate away evil.

But if you get rid of gun-free zones, you can kill evil, before it kills so many innocents.