Diaz has spent years writing about what he sees as the "clear and present danger" posed by the sale of powerful military sniper rifles to the public.
Among his fears: a pack of airliners lined up on an airport taxiway.
"One round of incendiary ammunition in the right place in a jetliner is going to cause it to burst into flames," Diaz said. "If it's next to another one, it's going to have what is called a fratricide effect, where one sits off another and another."
Investigators said they were "unable to identify any truly satisfactory solutions" to that threat.
Among Diaz's other concerns:
"Fuel tank depots. Worst of all, God forbid, toxic chemical storage -- where now you are talking about wind dispersion that could affect literally millions of people. This is all from one awesome, powerful weapon."
But what really makes the Barrett such a devastating weapon is its range: it's easily capable of hitting a target more than a mile away.
Gun rights advocate John Harris argues that the Barrett is exactly the type of weapon that the founders had in mind when they wrote the Second Amendment.
"They weren't protecting guns suitable for duck hunting or deer hunting or turkey hunting or sporting purposes," said Harris, who heads the Tennessee Firearms Association. "They were specifically protecting weapons suitable for military use."
Still, the Barrett .50-cal is now on the list of weapons that U.S. Dianne Feinstein, D-California, and some gun control advocates want to ban.
"I've often been accused of wanting to ban the Barrett and other .50-caliber anti-armor rifles -- I don't," Diaz said.
Instead, the gun control advocate said that they should be treated like machine guns, which would mean stricter background checks and a special license to own them.
"That doesn't mean you can't buy one," he said. "The same people who buy them now -- with the exception of the criminals and the terrorists -- could buy them in the future. But we would know who's got them."
For now, he noted that the Barrett .50 caliber and other similar rifles are less regulated than a .22 handgun.
To buy a handgun, you have to be 21. For the Barrett, it's 18.
Also, if a person buys multiple handguns, dealers nationwide have to report that to the feds, but the same rules don't apply to long guns.
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