"The Jews struck down all their enemies with the sword, killing and destroying them, and they did what they pleased to those who hated them. In the citadel of Susa, the Jews killed five hundred men. They also killed Parshandatha, Dalphon, Aspatha, Poratha, Adalia, Aridatha, Parmashta, Arisai, Aridai and Vaizatha, the ten sons of Haman son of Hammedatha, the enemy of the Jews. But they did not lay their hands on the plunder." NIV translation
In the capital city, the Jews also killed all of the sons of the man who had intended to kill the Jews. We notice that they did not do it for treasure as they did not take plunder. We must assume that this was an attempt to stamp out anti-Semitism (hatred of the Jews) but it is still alive even to this day.
"The number of those slain in the citadel of Susa was reported to the king that same day. The king said to Queen Esther, 'The Jews have killed and destroyed five hundred men and the ten sons of Haman in the citadel of Susa. What have they done in the rest of the king's provinces? Now what is your petition? It will be given you. What is your request? It will also be granted.'" NIV translation
The events of the day were reported to the king and he could see the power of the God of the Jews. He asked the queen what else was desired as he now knew that she was a woman of God.
"'If it pleases the king,' Esther answered, 'give the Jews in Susa permission to carry out this day's edict tomorrow also, and let Haman's ten sons be hanged on the gallows.' So the king commanded that this be done. An edict was issued in Susa, and they hanged the ten sons of Haman. The Jews in Susa came together on the fourteenth day of the month of Adar, and they put to death in Susa three hundred men, but they did not lay their hands on the plunder." NIV translation
Esther's request of the king was for vengeance and it was granted as Haman's dead sons were put on display by being hung on a gallows. This is a simple picture of the vengeance that God is going to take on those who mess with His children.