The megilla states that the second decree was that the Jews were allowed to defend themselves and that the original decree could not be revoked. It would appear that the people killed were the ones who took advantage of the first decree to attack the Jews. The implication is that the police were forbidden by the two decrees to interfere on an official basis, though it also appears that individuals could join the Jews on a personal level.
This would mean that everyone was given free rein on that day and would not suffer the penalty for murder.
The ten sons of Haman appear to have been the ones who were actively involved with their father in his plots. From the way it says that "they were hanged" and that they were left hanging on the second day, it would seem that they were hanged by the decree of Achashveros. Those killed by the Jews were not hanged, but killed in the fighting. That would be why they are separated in the megilla.
My son provided this Bonus Gematriah for Purim
1) 500 people were killed in Shushan, everywhere else, they killed 75,000 people
2) Achshveirosh ruled over 127 countries and if we assume Shushan was one of them, then it comes out that in the remaining 126 countries, they killed 75,000 people.
3) If you do the math (175,000/126), we see each country killed 595 people , which equals 74,970.
4) In Shushan they killed 500 + Haman. Haman is gematriah 95. So in every other country they needed to kill 595 to match what happened in Shushan.
5) You still have to account for an extra 30 people killed. (75,000‐74,970=30). The Medrash says Haman had 30 sons. 10 were hung, 10 were killed and 10 were beggars. We know a poor person is like a dead person. In order to make up the 30 sons killed, an extra 30 people were killed.