Radak on Zechariah
Say — They said "on the fifth and the severth" even though there are four fast days. It mentions the fifth because upon it was the destruction, and the seventh because in it Gedaliah was killed, and it was a second destruction, because already the poorest of the land remained and were not destroyed, since the poorest of the land were kept by Nebuzadaran to be vine dressers and ditch diggers (II Kings 25:12), but Gedaliah was killed on the first day of the seventh month, and since it was a holiday they declared a fast the day after.
Rashi on Zechariah
did you fast for Me, even for Me The ‘he’ is vowelized with a ‘hataf pattah’ because it is used as the interrogative: Did you fast in My honor that you should be required to fast now, too?