Ratliff, 32, was found Jan. 3 shot once in the head at the weapons development and testing facility he operated in Carnesville, Ga., WXIA reported.
The New York Times reportedthat Ratliff's body was surrounded by several guns at the scene, but not the one that killed him.
"For him not to pull out that gun and try to defend himself, he had to feel comfortable around somebody," Ratliff's brother, Kelly, told WSB-TV. "Either that or he was ambushed."
The Franklin County Sheriff's Office has called in Georgia Bureau of Investigation (GBI) agents to assist with the investigation, WXIA reported.
John Bankhead, the director of public affairs for the GBI told The Huffington Post:"There was no sign of a struggle."
A GBI spokesman also said the bureau is following up on several leads, but was asking for the public's help with information that might help solve the case.
Ratliff, and his partner, Kyle Myers, ran theFPSRussiachannel on YouTube, which showcases high-powered firearms and explosives. He also appeared on videos on his personal YouTube channel discussing firearms and trying out weapons at the request of viewers.
In onevideo, posted to Ratliff's personal YouTube account, he speaks out strongly against gun control, noting: "I am a gun nut."
"Every one of you should be able to own an assault weapon of your choice because that's what the Second Amendment is about," he says in the video clip. "It's about owning weaponry to allow you to defend yourself from all enemies, no matter where they rise from."
His death has prompted sharp exchanges on his YouTube page and other websites, with several commenters blaming the government for his death.
FPS is slang among video gamers for "First-person shooter."
The Russia in the name refers to the Russian accent used by Myers, who plays the character Dmitri Potapoff on the channel. The zany videos demonstrate the firepower of various weapons, usually in a dramatic fashion that involves dummies or objects being blown up.
(Copyright © 2013 USA TODAY)