CARNESVILLE, Ga. — 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.

Mr. Ratliff’s passion for firearms made him something of a celebrity on the Internet, where he helped make scores of videos about high-powered and exotic guns and explosives. His YouTube channel, called FPSRussia, became the site’s ninth largest, with nearly 3.5 million subscribers and more than 500 million views.

But last week, the authorities said, Mr. Ratliff, 32, ended up on the wrong end of a gun. The police in northeast Georgia found him dead at his office on Jan. 3, shot once in the head. He was surrounded by several guns, but not the one that killed him. The Georgia Bureau of Investigation is treating it as a homicide.

“We are interviewing people of interest, but we have not named a suspect,” said the Franklin County sheriff, Stevie Thomas. “We are not ruling out any options.”