The three suspects commonly cited are the purported danger of certain firearms, mentally ill individuals and modern forms of entertainment. They all make plausible culprits, until you look closely.
The first is our old nemesis the "assault weapon." The Newtown shooter used a Bushmaster semiautomatic rifle, which resembles a military model, and several 30-round magazines. President Barack Obama and several Democratic senators are therefore calling for a renewal of the "assault weapons" ban that expired in 2004.
But the guns they would ban are functionally identical to innumerable guns that would not be outlawed. Contrary to myth, these firearms don't produce bursts of automatic fire, don't "spray" bullets and aren't any more lethal than other semiautomatic guns. They are exceptional only in how they look.
What would a new ban achieve? As Reason's Jacob Sullum noted, Connecticut forbids the same assault weapons covered by the old federal law. Under its terms, however, the gun used by Adam Lanza was legal.
The gun-control advocates also want to prohibit high-capacity magazines, limiting them to 10 rounds. The lifesaving value of this change is likely to be close to zero. Ordinary street thugs rarely fire many rounds, and those intent on slaughtering large numbers of victims can carry multiple magazines and multiple guns. That's exactly what Lanza did.
The theory is that a shooter who has to pause to reload can be stopped. But switching out a magazine takes only seconds. Florida State University gun scholar Gary Kleck says he knows of only one case where bystanders overcame a mass shooter when he stopped to reload.
Jared Loughner, who killed six people in Tucson, was tackled only after reloading, when his gun jammed. Lanza, shooting docile first graders in a confined space, didn't have to worry they would subdue him.
Many of the suggestions for averting the next massacre involve how we handle the mentally ill. Sen. Dick Durbin, D-Ill., called for denying guns to "those with a history of mental instability."