Currently the term "Truther" refers to someone who adheres to the beliefs espoused by the 9/11 Truth movement. Truthers are conspiracy theorists that, like all conspiracy theorists, blatantly distort facts and quotes. These are the Bible thumpers
Some of them believe that the government orchestrated it in some complex, cockamamie scheme; others believe that the government simply let it happen.
Debating a Truther is like banging your head against a brick wall - painful and futile. You are likely to be called many things by them: ignorant, stupid, sheltered, blind, scared of the truth, a sheep, a lemming.