The only thing that lends credibility to the story in the post you're responding to is the person who's claiming it's the truth. Seymour Hersh [1] has enough of a track record that we shouldn't dismiss it out of hand. As far as evidence goes, I'm not sure the official story has been proven any more than Hersh's story has, so it's hard to know what to believe.
[1] https://en.wikipedia.org/wiki/Seymour_Hersh