Starfleet didn't sanction killing the senator, just forging the record. That other bit was all Garak; I doubt Sisko told Starfleet about that part, considering the end of the episode.
True, and Sisko not telling Starfleet is a possibility, but their hands are pretty dirty under the "Clean Hands" doctrine.
When the Romaulans eventually went to war and lost millions (as the series seems to claim) that achieved the same effect as genocide.
Mainly because it was engineered by Starfleet to happen.
If they forged any records dealing with this it amounts to a cover up.
So, you hold Starfleet accountable for every rogue officer?
Star Trek TUC is a doozy.
An example of Starfleet conspiring against political figures, their own officers, considering a pre-attack against a power calling for peace discussions, willing to look away while that power faces planet-wide catastrophe.