How would you like the comment to be qualified? Most direct public confirmation I can think of would be the IG report regarding violations, I believe it was one of the Snowden documents, in which multiple people who tried to “test” search themselves or others and it failed to allow the query (They were disciplined either way, of course).

I don’t think there was a claim to the contrary, unless you’re thinking of targeted / secret FISA by FBI, which is a different issue yet a possibly valid point (due to lack of normal search warrant).