2. These are the [public fast] days: The third of Tishrei, the day on which Gedaliah ben Achikam was murdered. After the destruction of the [first] Beit Hamikdash (Temple) (1), Nebuchadnezzar (2) had left [Gedailiah] in the Land of Israel, and appointed him as the head of the [remnants] of the Jewish people [who were still living there] (3). After he was murdered, the entire populace was exiled, thousands [more] were killed, and the spark of Israel that remained [in the Holy Land] was extinguished (4).
(1) Destroyed in 422 BCE
(2) Ruler of the Babylonian Empire, who's army destroyed the first Beit Hamikdash.
(3) Most of the Jews had been exiled to Babylon.
(4) For the full story, see II Kings Chapter 25, and Jeremiah Chapters 39,40 and 41.