For instance, there was no child molestation at Waco, yet people think there was. (nor were they suicidal. Koresh, when he heard the ATF was asking about him in town, called up the local ATF office and asked to set up a meeting so he could answer any questions they had. Yet, the media reports that he was "hiding out" necessitating the "raid" on the "compound".) I picked waco as an example because it is long enough ago that maybe it can be considered objectively.
The day of the incident is when spin is the most effective. Getting out the "official story", even if it turns out to be absurd or outright false in retrospect, is paramount. It doesn't matter when the truth comes out-- most people will never hear it, and many who do won't believe it because the person spreading it, no matter how much evidence they have, is going against the "official story" and therefore is a "conspiracy theorist" and thus has no credibility.
This is how the public is manipulated into believing disprovable things.