UPDATED: Sept. 24, 2014 4:55 p.m.

WASHINGTON — The number of shootings in which a gunman fired into a crowd has increased dramatically in recent years, according to an FBI report released Wednesday.

The study reviewed 160 mass shootings between 2000 and 2013 to identify common themes and to help local law enforcement prepare for or respond to similar killings in the future.

It focused on what the FBI calls “active shooter incidents,” cases in which a gunman in an attack kills or shoots multiple people in a confined space.

According to the report, an average of six shootings occurred in the first seven years that were studied. That average rose to 16 shootings per year in the past seven years of the study. That period included the 2012 shootings at a movie theater in Aurora, Colorado and at Sandy Hook Elementary School in Newtown, Connecticut.

Most of the shootings occurred either at a business or a school, according to the study, conducted in conjunction with Texas State University. A total of more than 1,000 people were either killed or wounded in the shootings. In about one-quarter of the cases, the shooter committed suicide before the police arrived.

Law enforcement officials who study the behavior of shooters and assess threats say the motives vary but many have a real or perceived personally held grievance. Though it’s hard to say why the number of shootings has increased, officials say they believe many shooters are inspired by past killings and the resulting notoriety.

“The copycat phenomenon is real,” said Jerome Simmons, an FBI behavioral analyst. “As more and more notable and tragic events occur, we think we’re seeing more compromised, marginalized individuals who are seeking inspiration from those past attacks.

The report excludes shootings that are gang- or drug-related, as well as shootings that involve self-defense.

Beyond studying the shootings, the FBI has promoted better training for local law enforcement, invariably the first responders.

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