On Monday Aaron Alexis, 34, who worked there for a private contractor, shot and killed 12 people at the Washington Navy Yard.

There seems to be an epidemic of mass shootings -- in Tucson, Arizona in 2011, last year in a movie theater in Aurora, Colo., and in an elementary school in Newtown, Conn.

Appearances are deceiving. In the 30 years ending in March, there were 78 mass shootings, said the Congressional Research Service. CRS defines a mass shooting as an incident "in which four or more people were killed at random by a gunman killing indiscriminately."

In these mass shootings, 547 people were killed. The FBI estimates that in the 30 years ending in 2012, 559,347 people were murdered. The 547 slain in mass shootings account for less than one-tenth of 1 percent of these murders. Many more die in collisions with deer.

Even one is too many if it could have been prevented. The Navy Yard shooting had these things in common with those earlier:

• The shooter was mentally ill. Aaron Alexis was being treated by the Veterans Administration for PTSD, sleep disorders, paranoia. He "heard voices." He had a history of violent behavior, had been involved in two earlier shooting incidents.

• The shooter chose a venue where he knew his victims would be unarmed. By decree of President George H.W. Bush in 1992, military bases are, in effect, "gun free" zones -- like elementary schools (Newtown), high schools (Columbine), colleges (Virginia Tech), and movie theaters (Aurora).

• Initial news coverage was awful. Two networks gave the wrong name for the killer. Many news organizations reported, falsely, the shooter used an AR-15 rifle. (Alexis did his killing with a shotgun -- the firearm Vice President Joe Biden recommended for home defense -- and with two pistols he took from security guards he killed with his shotgun.)

This is, alas, typical. Because the Tucson shooting took place at a town meeting held by Rep. Gabrielle Giffords, D-Ariz, many journalists blamed it on a "climate of hate" produced by "right-wing vitriol." (The shooter, Jared Loughner, was mentally ill. He had a bizarre personal grudge against Ms. Giffords, but no discernible political motive. His politics, such as they were, were left- wing, said a former classmate.)

ABC's Brian Ross falsely accused a Tea Party member of the movie theater shooting in Aurora.

Many news organizations fingered the wrong guy in the Connecticut school shooting. Also reported erroneously were Adam Lanza's connection to the school, how he gained entry and the guns he used in his murder spree.

This happens over and over mostly because many journalists would rather be first than be right. Cable news anchors are the worst offenders. When something bad happens, people tune in to find out what's going on. The anchors don't know. Rather than admit that -- and risk losing their suddenly swollen audiences -- they "report" rumors and gossip, and speculate.

Errors are compounded by ignorance (a CNN anchor said Alexis was armed with an "AR-15 shotgun,") and because so many journalists have an agenda they push without regard to the facts.

"Nothing that gun-control advocates are pushing for in Congress would have prevented Monday's rampage at the Washington Navy Yard," noted the National Journal.

Here's what might have:

The mentally ill who are potentially homicidal used to be committed to state mental hospitals. After a "de-institutionalization" campaign led by liberals that peaked in the 1970s, most of those hospitals have closed. Roughly 200,000 schizophrenics and others who would have been in them are instead in prison (16 percent of those in jail or prison are mentally ill) or living on the streets. For those in Tucson, Aurora, Newtown or the Navy Yard, they don't go to prison until after they've committed a crime.

Liberals should rethink "de-institutionalization" and ponder why mass murders nearly always take place in "gun-free zones." Since 1997 there have been at least nine mass murders you didn't read about, because an armed citizen cut the murder spree short.

Adjacent to the Navy Yard is the Marine Barracks. "If we had ammunition, we could have cleared that building," the father of a Marine stationed there said he was told by his son. "Only three people had been shot at that time, and they could've stopped the rest of it," the father said to Dan Joseph of the Media Research Center.