Guns.

Philip Markoff, a medical student, supposedly carried his semiautomatic in a hollowed-out volume of “Gray’s Anatomy.” Police believe he used it in a hotel room in Boston last week to murder Julissa Brisman, a 26-year-old woman who had advertised her services as a masseuse on Craigslist.

In Palm Harbor, Fla., a 12-year-old boy named Jacob Larson came across a gun in the family home that, according to police, his parents had forgotten they had. Jacob shot himself in the head and is in a coma, police said. Authorities believe the shooting was accidental.

There is no way to overstate the horror of gun violence in America. Roughly 16,000 to 17,000 Americans are murdered every year, and more than 12,000 of them, on average, are shot to death. This is an insanely violent society, and the worst of that violence is made insanely easy by the widespread availability of guns.

When the music producer Phil Spector decided, for whatever reason, to kill the actress, Lana Clarkson, all he had to do was reach for his gun  one of the 283 million privately owned firearms that are out there. When John Muhammad and his teenage accomplice, Lee Malvo, went on a killing spree that took 10 lives in the Washington area, the absolute least of their worries was how to get a semiautomatic rifle that fit their deadly mission.