Lanza did not have the sort of psychiatric (or criminal) history that would have disqualified him from owning firearms, which is one reason why strengthening the background-check system for gun buyers makes no sense as a response to the Sandy Hook massacre. Another reason: "All of the firearms were legally purchased by the shooter's mother."
The Connecticut legislature has since banned the rifle Lanza used, a Bushmaster XM-15-E2S. But the ban does not apply to guns owned before it took effect, and equally lethal weapons remain legal.
Connecticut's new 10-round limit on magazines likewise exempts equipment already in circulation. Even if it didn't, the limit's relevance to Lanza's attack is debatable.
According to Sedensky's report, Lanza fired 154 rounds over five or six minutes -- about one round every two seconds. That is not a particularly fast rate of fire, and there is little reason to think it would have made a significant difference if Lanza somehow had been compelled to use 16 10-round magazines rather than six 30-round magazines.
When Lanza shot himself in the head, a minute before the first police officer entered the school, he still had almost 300 rounds for the rifle and the two pistols he was carrying. That suggests ammunition was not a limiting factor.
Easy answers are appealing in the wake of such a horrifying crime. But one year later, we should recognize the folly of trying to explain the inexplicable or prevent the unpreventable.