Just because someone attends church doesn't mean they are extremists that need to be investigated by the FBI.
Maybe 9% of US citizens do not believe in God. Another vocal minority that should just STFU.
Religious Group
According to sociologists as of 2022, "the proportion of atheists in the US has held steady at 3% to 4% for more than 80 years." According to the Pew Research Center in a 2014 survey, self-identified atheists make up 3.1% of the US population, even though 9% of Americans agreed with the statement "Do not believe in God" while 2% agreed with the statement "Do not know if they believe in God".
Wikipedia