WASHINGTON — School shootings are rare. Between 1963 and 1990, there were an average of 18.6 deaths a year from such violence. Since 1990, however, there have been 168 mass shootings, defined as those involving four or more people, although that is an inexact and controversial measure.
The last confirmed mass shooting was at Marjory Stoneman Douglas High School in Parkland, Fla., where 17 students and educators were killed on Valentine’s Day.
Police responding to the incident on Monday arrested the suspect, 19-year-old Nikolas Cruz, who was charged with 17 counts of premeditated murder. The incident prompted politicians and education officials to raise questions about what can be done to stop such violence. The U.S. Education Department recently responded to a public call to provide greater transparency about the number of school shooters.
Cruz’s attorney said the suspect may have been dealing with mental health issues related to being adopted and bullied. It’s not clear whether he had access to a gun, since he faces allegations of murder.
In 2012, the Obama administration advocated tougher background checks on gun purchases and a broader discussion about how to address the problem. In 2013, after a man shot to death six elementary school students and one teacher in Newtown, Conn., the White House responded by proposing significant tightening of gun regulations and a national discussion about how to prevent such attacks.
But such efforts have consistently failed to gain traction in Congress. And there hasn’t been nearly enough public debate about how to address school shootings. There are many unanswered questions about exactly what went wrong, and it could take months before answers emerge.
Here’s a look at the history of school shootings and the odds that someone could be prosecuted if charged in a case like this.
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How common is school shooting?
Most shooting incidents in school districts don’t result in charges. The vast majority of the school shootings in American history happened before the 1990s, during which time there were an average of only four. The number of shootings increased with the passage of more lenient gun laws, in part because more guns meant more shots being fired. After the 1994 enactment of the Brady bill, for example, the rate of yearly mass shootings in the U.S. decreased from an average of 17 to six.
But since 1990, a window has opened for criminal prosecution of shooters. Violent incidents involving four or more people are more likely to result in charges being filed than are those involving three or fewer.
Some school shootings have resulted in charges against teachers. A teacher at Upstate New York’s Fayetteville-Manlius High School, for example, was charged in April 2010 for planning to kill as many students as possible. The suspect’s grandfather died the same day, and the shooting was seen as revenge. The teacher, Mark Black, had already committed suicide.
More than 70 school shootings have resulted in some type of criminal charge, with many more requiring a pretrial intervention program. The wide range of criminal charges has kept the case from being a matter of clear-cut debate.
What kind of crime does a school shooter often commit?
Even violent incidents involving four or more people can be reduced to a misdemeanor by presenting mitigating factors, including that the defendant is only 17 years old, has no history of violent behavior and does not have other criminal charges pending against him.
What is the likelihood of prosecution?
Six years after Columbine High School in Colorado, the U.S. Bureau of Justice Statistics found that mass shooters are almost always charged with crimes or misdemeanors.
Seven mass shootings occurred in 1991, accounting for half of the 112 school shootings that year. The largest number, 25, took place that year. Some of the shootings occurred in empty classrooms, while others involved students or educators fighting with each other. The smallest number, three, took place that year.
There have been more school shootings every year since 1991, except for a few years when they were the subject of media saturation. The number of shootings never dipped below 10 for several years after 1993.