Why AR-15-style rifles are popular among mass shooters

George Frey/Getty Images(NEW YORK) -- When suspected gunman Nikolas Cruz mowed down at least 17 adults and students at Florida’s Marjory Stoneman Douglas High School on Wednesday, he was armed when an AR-15-style rifle that he purchased legally.

AR-15-style rifles have become something of a weapon of choice for mass shooters. One was used last year to kill 26 people during Sunday-morning church services in Sutherland Springs, Texas. And it was among the stockpile of firearms used a month earlier to kill 58 concertgoers in Las Vegas.

AR-15-style rifles were also used at the shootings at Pulse nightclub in Orlando, Florida; at an employee training in San Bernardino, California; and at Sandy Hook Elementary School in Newtown, Connecticut.

So why is this type of weapon so popular among mass shooters? Gun experts told ABC News it has nothing to do with the AR-15's lethality, but rather simple familiarity.

“In the U.S., our go-to rifle is the AR-15. It’s known as the American rifle,” former SWAT team member and gun expert Dean Hazen said. “Most police departments carry it; our military carries a militarized version of it. In some mass shootings, the shooter had low knowledge of firearms. They just grabbed what they know, and that’s the AR-15.”

Pete Blair, executive director of Texas State University’s Advanced Law Enforcement Rapid Response Training Center -- which studies mass murder -- echoed Hazen's comments.

“The AR is the most popular rifle platform in the U.S.,” Blair said.

The fact that so many mass shooters are using the same gun is what sociologists call “social proof,” he added.

Hazen said this phenomenon takes place when one is in an "ambiguous" situation and don't know how to proceed. "That can be looking at what silverware other people use at a fancy dinner party and copying them, or it can be using the same type of weapon other shooters have used if you’re planning a mass shooting.”

Hazen added, "It’s a copycat thing. When they see other mass shooters use it, it reinforces the image in their mind that this is the evil tool to use.”

The NRA said the AR-15 has “soared in popularity” because it is “customizable, adaptable, reliable and accurate” and “can be used in sport shooting, hunting and self-defense situations.”

Blair doesn’t believe those are the reasons why mass shooters are choosing the AR-15, though.

“I don’t see a lot of customization happening with the guns mass shooters use. They’re pretty much using the stock AR, which is easy to operate and straightforward,” Blair said.

Copyright © 2018, ABC Radio. All rights reserved.

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