Possible Clues:

• I don't believe first letter's the first!
• Person who does not believe in existence of a god
• One not believing in gods
• One beyond belief?
• O'Hair, famously
• A believer or otherwise
• One doesn't believe cook heats it
• One article after another is on rat's tail - but he doesn't believe it
• Albert Camus or Isaac Asimov, religiously
• One doesn't believe suspect ultimately involved in a crime