I'm just taking him at face value, and playing devils advocate somewhat. Also I'm a conspiracy head, and over time the "they could never have kept it a secret" argument just seems weaker and weaker to the point where it seems naive. Many very large conspiracies have been kept secret to great degree, despite the involvement of many people in them. Compartmentalization, need-to-know, hierarchy, NDAs etc.

I will say that usually very few of the people involved seem to know the whole story, which is still the part where I'm suspicious of this guy, since he seems to be saying a Doctor involved told him all this.