In what way are stories like this one less "credible" than accounts of Assad using poison gas? Since neither the neocons nor their opponents were eye-witnesses to either, you'd think that they would be equally credible (or incredible).
In fact, "credible" just means "serving the interests of our agitprop."
I think you meant Marxists. There is no such thing as a neocon. Neocon means a new conservative which allegedly were the southern democrats which discriminated against the blacks back in the day. I believe there was actually one of those racist democrats that converted to the republican party and he died years ago. The remaining racist democrats were racist democrats all the way to their graves.