After the destruction of the Temple, Nebuzaradan, captain of the Babylonian guard under Nebuchadnezzar, found blood bubbling up from the ground in Jerusalem. According to Gittin 57b, he demanded to know whose blood it was.
The people of the Temple told him it was sacrificial blood. He tested it against animal blood. It did not match. He threatened them with iron combs. They confessed: it was the blood of the prophet Zechariah ben Jehoiada, whom they had murdered for rebuking them. His blood had been bubbling for years, refusing to settle—as the verse records: "The spirit of Zechariah clothed him, and he stood above the people and said to them: Thus says God—why do you transgress?" (II Chronicles 24:20).
Nebuzaradan tried to appease the blood. He killed the members of the Great Sanhedrin (the supreme rabbinic court) and poured their blood alongside it. The bubbling continued. He killed the members of a lesser court. Still bubbling. He killed young men and women. Still bubbling. He killed schoolchildren. Still bubbling.
Finally he spoke directly to the dead prophet: "Zechariah, Zechariah. I have killed the best of them. Would it please you if I destroyed them all?" At that moment, the blood settled.
The horror of it shook Nebuzaradan to his core. He reasoned: if God punished the Jewish people this severely for the death of one prophet, then he—who had killed thousands—would surely face even worse. He fled. He sent instructions home for his property to be distributed. And he converted to Judaism.
The passage ends with a startling genealogical note. Descendants of Israel's greatest enemies became Torah scholars. Some of Haman's descendants studied Torah in Bnei Brak. Some of Sisera's descendants taught children in Jerusalem. Shemaya and Avtalyon, the great teachers of Hillel, were descendants of Sennacherib. The murderers' bloodlines produced the sages who rebuilt what their ancestors destroyed.