The bombing of Keiko O'Brien's schoolroom on Deep Space 9 during a dispute over teaching about the wormhole, part of a plot to lure Vedek Bareil to the station and assassinate him.
In the Deep Space Nine episode In the Hands of the Prophets, Vedek Winn arrives on the station and denounces Keiko O'Brien for teaching that the wormhole's inhabitants are aliens without speaking of them as the Prophets. Bajoran families withdraw their children, traders refuse to serve the O'Briens, and the school is wrecked by an explosion while empty.
At the same time Miles O'Brien finds the remains of Ensign Aquino in a power conduit and suspects murder. Sisko visits Vedek Bareil, the liberal favourite to become Kai, who agrees to come to the station to ease tensions.
That visit was the purpose of the whole affair. O'Brien's trusted Bajoran assistant, Neela, has disabled the security systems and killed Aquino when he caught her. She draws a weapon on Bareil on the Promenade, and Sisko knocks her aside. Winn's part can never be proved.