Indians For Guns

WASHINGTON — A report released by the F.B.I. on Wednesday confirmed what many Americans had feared but law enforcement officials had never documented: Mass shootings have risen drastically in the past half-dozen years.

There were, on average, 16.4 such shootings a year from 2007 to 2013, compared with an average of 6.4 shootings annually from 2000 to 2006. In the past 13 years, 486 people have been killed in such shootings, with 366 of the deaths in the past seven years. In all, the study looked at 160 shootings since 2000. (Shootings tied to domestic violence and gangs were not included.)

Many of the sprees ended before the police arrived, the report said. In 44 of the 64 cases in which the F.B.I. was able to determine the length of the shooting, the gunfire lasted less than five minutes. Twenty-three shootings ended in less than two minutes. In 64 of the 160 total cases, the gunmen committed suicide.

The report was prompted by the spate of mass shootings in recent years, like those at Sandy Hook Elementary School in Connecticut and at a movie theater in Aurora, Colo.

After the Sandy Hook massacre, in which 20 children were killed, President Obama announced that administration and law enforcement officials would study how the country could stop the shootings from occurring.

There was a widespread belief that the number of shootings had risen significantly, but the federal government had no uniform way of tracking them. As part of the administration’s efforts, the F.B.I., which keeps track of national crime statistics, was asked to determine whether the shootings had increased. The report was the first time that the federal government had determined the number of mass shootings over a significant period of time, according to the F.B.I.

Academics had previously tried to quantify mass shootings by using news media reports. In the new study, the F.B.I. relied on court documents, reports from all of its 56 field offices, and news media reports. The team of agents and analysts who worked on the study said they would use the numbers as a baseline in studying other shooting trends.

The report raised questions about the effect the mass shootings are having on law enforcement officers who respond to the grisly scenes. It also reinforced one of the recommendations from the administration’s study: that local officers need to be better trained and equipped to stop gunmen intent on slaughter.

In 21 of 45 shootings in which officers confronted the gunmen, nine officers were killed and 28 were wounded. Four officers were killed in ambushes, and in three cases, armed security guards who were not law enforcement officers were killed. In two other shootings, two unarmed security officers were killed and two were wounded.

Officers killed the gunmen at the scene in 21 of the cases. Nine gunmen who exchanged fire with the police committed suicide, and two surrendered.

Just two of the 160 shootings involved more than one gunman, and six of the killers were women. Two of the twelve shootings that occurred at colleges or universities were by women.

Roughly 45 percent of the shootings occurred in offices or stores, and about 25 percent at schools or universities. Other sites included military bases, government offices, homes, places of worship and medical facilities. In 24 of the 160 shootings, the gunmen attacked more than one location. Mass shootings occurred in all but 10 states.

The most deadly shooting occurred at Virginia Tech in 2007. In that shooting, 32 people were killed and 17 were wounded. The most injuries — 58 of them — resulted from the shooting at the Aurora, Colo., movie theater, where 12 people were killed.

F.B.I. analysts said that many of the gunmen had studied high-profile shootings, like the one at Columbine High School in Colorado in 1999, before going on their own killing sprees.

The analysts said the gunmen had been attracted to the attention that mass killers received. They were often motivated by a sense that they had no other way to resolve the issues they faced other than violently lashing out, the analysts said.