How did Charbano know about the pole that Haman prepared for Mordechai?
Torah Temimah citing Megilah 16a: Also Charbano ha'Rasha was initially part of the Etzah 1 . Now that he saw that it was failing, he fled. "Va'Yashlech Alav... mi'Yado Baro'ach Yivrach" (Iyov 27:22; when Hashem punishes a Rasha, his entire company deserts him).
Vilna Gaon, Malbim: He was one of the Sarisim sent to bring Haman to the Mishteh [and heard Haman talking with his advisors].
Vilna Gaon: I.e. he was one of the Sarisim sent to bring Haman to the second Mishteh (6:14). A Saris always serves in front of the king. How else would he know?! (He does not explain that he was one of Haman's beloved who counseled him to make the pole, for Charbano always serves the king - how would he be in Haman's house to counsel him? Rather, when he went to bring Haman, he heard [amidst Haman talking with his advisors] that Haman made it for Mordechai. However, 'Etzah' implies counsel. And why is Charbano called a Rasha? Also the verse in Iyov implies that Charbano was helping Haman! - PF) Magihah in Perush ha'Gra ha'Shalem - perhaps the Vilna Gaon's words should say, after citing the Gemara, 'but one could explain simply that he was one of the Sarisim.'
Why did he say "Gam"?
Rashi: He did also another evil - he prepared a pole to hang the king's beloved, who saved the king from poison!
Malbim: Also Haman was part of the plot to poison Achashverosh. He was upset that Mordechai saved the king, therefore he wanted to hang him.
Why did he say "Hine ha'Etz"?
Vilna Gaon: Because it was so tall, one could see it from Beis ha'Melech, like I explained (5:14:1:1).
Malbim: This is a great disgrace to the king. He dressed Mordechai in royal clothing, and announced that the king desires his honor, and Haman's pole to kill him is exposed for all to see! This is the ultimate rebellion.
What is the significance of "Asher Diber Tov Al ha'Melech"?
