There's no such thing as a devout atheist.
And again, there is no proof of the existence of Jesus.
The authenticity of the inscription on the James Ossuary is still up in the air, as is who it is referring to. Those names were not exactly particularly rare back then.
The origin of this item that came out of nowhere is also bit suspicious, the owner claiming he bought it and just tucked it away for several years not realizing what the inscription said.
He has also been accused forging the inscription, even convicted for it, although said conviction was thrown out as it was not proven that he had forged it.