I believe that some Kenyan officials were BRIBED to release the thuth - the evidence.
I doubt anyone had to be bribed. The Kibaki government has every reason in the world to cut down Obama... who actively campaigned against them in favor of the ODM socialist Odinga (who also claims to be Obama's cousin).
Odinga and his thugs butchered their way to a power sharing arrangement after losing a close election (Kibaki as President, Odinga as Prime Minister). It makes sense that Kibaki would want to take out his archrival's most powerfully ally and solidify his position in Kenya.
Well, it's fun to speculate about the back-story, but we need to keep that sort of thing in perspective. In time, the story of where this came from, and how it was obtained will surely come out.