(CNN) — Mass shootings such as the one Wednesday in San Bernardino, California, often produce initial reports of multiple gunmen, likely owing to the confusion and chaos that immediately follow gunfire.
The reality, though, at least in the United States, is that mass killings rarely involve multiple shooters.
Of the 28 deadliest shootings in U.S. history before Wednesday — from Howard Unruh’s 1949 rampage in Camden, New Jersey, to Christopher Sean Harper-Mercer’s killing spree at Umpqua Community College in Roseburg, Oregon, in October — only two have come at the hands of multiple shooters: the February 1983 killings at the Wah Mee gambling and social club in Seattle and the Columbine High School massacre in Littleton, Colorado, in 1999.
In Seattle, Kwan Fai Mak, Benjamin Ng and Wai-Chiu “Tony” Ng robbed 14 patrons of the gambling parlor before shooting each of them in the head. Thirteen of the victims died; the other survived to testify against the shooters. In Columbine, teenagers Eric Harris and Dylan Klebold killed a dozen fellow students and one teacher before committing suicide in the school library.
Such historical data reinforces the highly unusual nature of the fatal shootings of at least 14 people in San Bernardino, where police Wednesday afternoon were seeking three suspects armed with AK-47-type weapons. The suspects were thought to have escaped in a dark-colored SUV.
The FBI has found that of 160 “active shooter” incidents in the United States between 2000 and 2013 — defined as a situation where law enforcement is responding to a shooting in progress — all but two involved a single shooter.
While mass shootings by lone gunmen are often premeditated, killings by multiple shooters can suggest a higher level of planning, law enforcement officials say.
“They came prepared to do what they did, as if they were on a mission,” San Bernardino Police Chief Jarrod Burguan said at a news conference. Police did not offer a possible motive for the shootings.