On Feb. 14, a shooter pulled a fire alarm at a South Florida high school and waited for his victims to pour into the halls.

Armed with an assault-style weapon, he opened fire, killing at least 17 adults and children and leaving others injured.

Early Thursday, teenage suspect Nikolas Cruz was booked on 17 counts of “murder premeditated.” Cruz, 19, had once attended the high school. He was expelled from Marjory Stoneman Douglas High School for disciplinary problems. His father died a few years ago, and his mother, among the only people with whom he was close, died around Thanksgiving. He was living at a friend’s house and showing signs of depression.

The shooting, which occurred in Parkland, Fla., is the nation’s second deadliest public school shooting. Cruz, the suspected shooter, had a fascination with guns.

The places and numbers change, but when people want to kill others in the United States, the choice of weapon remains the same.

Public mass shootings account for a tiny fraction of the country’s gun deaths. In 2018 so far, mass shootings have resulted in 21 deaths, compared to 1,827 deaths from gun-related incidents, according to the Gun Violence Archive and Washington Post research.

But public mass shootings are uniquely terrifying because they occur without warning in the most mundane places. Most of the victims are chosen not for what they have done but simply for where they happen to be.

What is a public mass shooting?

There is no universally accepted definition of a public mass shooting. This piece looks at the 150 shootings in which four or more people were killed by a lone shooter (two shooters in a few cases). It does not include shootings tied to gang disputes or robberies that went awry, and it does not include shootings that took place exclusively in private homes. A broader definition would yield much higher numbers.

The tally begins on Aug. 1, 1966, when a student sniper fired down on passersby from the observation deck of a clock tower at the University of Texas. By the time police killed him, 17 other people were dead or dying. There have been 149 additional public mass shootings since then.

In the 50 years before the Texas tower shooting, there were just 25 public mass shootings in which four or more people were killed, according to author and criminologist Grant Duwe. Since then, the number has risen dramatically, and many of the deadliest shootings have occurred within the past few years.

The victims

Including that day in 1966, 1,077 people were killed in public mass shootings in the United States.

• Among the victims, 162 were children and teenagers.

• Thousands of survivors were left with devastating injuries, shattered families and psychological scars.

• The oldest victim was Louise De Kler, 98, who was shot to death in 2009 by a man who had come to her Carthage, N.C., nursing home looking for his estranged wife.

• Among the youngest victims is Carlos Reyes. At 8 months old, he was buried in a casket with his mother, Jackie, who had tried to shield him as an unemployed father of two opened fire at a busy McDonald’s in San Ysidro, Calif., in 1984. Two unborn children are included in the official death tolls from shootings in Austin and Sutherland Springs, Texas.

The shooters and their weapons

The number of shooters stands at 153. Some of these mass shooters were known to have violent tendencies or criminal pasts. Others seemed largely fine until they attacked.

• Shooters often carried more than one weapon; one was found with 23.

• At least 167 of mass shooters’ weapons were obtained legally and 49 were obtained illegally. It’s unclear how 76 weapons were acquired.

• Semiautomatic rifles have been used in some of the country’s deadliest shootings, such as those in Newtown, Orlando, San Bernardino and Las Vegas. The AR-15, a lightweight, customizable version of the military’s M16, soared in popularity after a federal ban on assault weapons expired in 2004.

• All but 3 of the shooters were male. The most recent female shooter was a Pakistani mother who helped kill 14 partygoers at her husband’s workplace in San Bernardino, Calif., in 2015. The others are an ex-postal worker who killed a former neighbor and six employees at a Goleta, Calif., mail-processing facility in 2006; and a former tribal council chairwoman who killed her brother and three others during an eviction hearing in Alturas, Calif., in 2014.

• The vast majority were between the ages of 20 and 49.

• More than half — 88 of them — died at or near the scene of the shooting, often by killing themselves.

Where do public mass shootings occur?

They can happen anywhere. Since 1966, public mass shootings have occurred in 41 states and the District of Columbia. Shootings in schools and houses of worship tend to stick in our minds, but they make up a relatively small portion of mass shootings. More common are those in offices and retail establishments such as restaurants and stores. California has had more mass shootings than any other state, with 23.

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