The gun enthusiast with the 11th most popular channel on YouTube -- who insisted everyone has the right to an assault weapon under the Second Amendment -- was shot and killed in what's been described as his Georgia "weapons development and testing facility" last week.

Keith Ratliff died, according to reports, from a single shot to the head -- but the murder weapon can't be found, and there was no sign of a struggle.

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And all that has confused police in Georgia -- who have called his death a homicide -- and Ratliff's millions of fans and followers, who have poured out sadness and confusion on Twitter and Facebook that he was not able to fight back and defend himself.

As USA Today reports, Ratliff's brother, Kelly, told an Atlanta TV station that "For him not to pull out that gun and try to defend himself, he had to feel comfortable around somebody. Either that or he was ambushed."

But as the Huffington Post reports, the Georgia Bureau of Investigation says there was no sign of a struggle at the Carnesville, Ga., store where Ratliff repaired firearms. (He was registered with the ATF.)

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It was online, however, that Ratliff was a celebrity within the gun-rights movement. His YouTube channel, FPS Russia, has almost 3.5 million subscribers, according to the New York Times, and has been viewed some 500 million times. FPS stands for first-person shooter; the Russia refers to partner Kyle Myers, who plays a character in the videos who speaks with a Russian accent.

Lots of things blow up in the videos, as USA Today notes: "The zany videos demonstrate the firepower of various weapons, usually in a dramatic fashion that involves dummies or objects being blown up." Those objects might be bales of hay, or photos of Justin Bieber. (That video is called "Shooting Justin Bieber with F2000.")

In a recent "gun control rant" on his personal YouTube page, as the national debate over weaponry picked up after Newtown, he called himself a "gun nut" and insisted that the Second Amendment is "about owning weaponry to allow you to defend yourself from all enemies, no matter where they rise from."

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According to the Times, "Keith Ratliff loved guns. He built his own rifles. He kept bullets in his car’s cup holder. And on the rear window he slapped a sticker of the Starbucks Coffee mermaid firing two pistols. 'I ♥ Guns and Coffee,' it read."