Rava said: Nebukhadnezzar sent Nevuzaradan three hundred mules laden with iron axes that could break iron, but they were all shattered on a single gate of Jerusalem. Although Nevuzaradan was ready to retreat, he feared that he would be killed as was Sanḥeriv before him. At that time, a heavenly voice called out to him that the time has come for the Sanctuary to be destroyed and the Temple burnt. He had but one axe left, so he went and struck the gate and it opened. Killing Jews as he went, he reached the Temple, which he set afire. He was elated with his triumph, but again a heavenly voice came down saying to him, ‘You have killed a dead people, you have burned a Temple already burned, you have ground flour already ground.’
Entering the Temple precincts, he saw the blood of the navi Zekhariah boiling. He demanded of the kohanim to be told what this was and they answered ‘It is the blood of sacrifices, which has been spilled.’ He instructed them to bring some animal blood so that he could compare them. He insisted that they tell him the secret, threatening to flay their skin with iron combs. Finally the kohanim told him that this was the blood of a priest and a prophet, who foretold the destruction of Jerusalem to the Israelites, and they killed him.
Intent on “pacifying” his blood, Nevuzaradan brought the Sages and slew them over him, yet it did not cease to boil. He brought schoolchildren and slew them over him, still it did not rest; he brought the young kohanim and slew them over him, and still it did not rest, until he had slain nine hundred and forty thousand, and still it did not rest. Whereupon he approached him and cried out, ‘Zekhariah, Zekhariah, I have destroyed the worthy among them, do you want me to massacre them all?’ At that time the blood rested. At that time Nevuzaradan decided to repent saying ‘if they, who killed one person only, have been so severely punished, what will be my fate?’ So he fled, and converted.
In conclusion the Gemara shares a tradition that Nevuzaradan was a righteous convert.
The threat to flay their skin with iron combs would have been carried out with a harpago, a metal comb that was used as an instrument of torture into the Roman period.