1)
Who are "Nesi'ei Yisrael"?
1.
Radak: The kings and the officers.
2.
Malbim: They are those who were chosen to be over them due to their level. A nation can fix its deeds via heeding them. Here they will not accept the Nesi'im's teaching, for the Nesi'im themselves murder via force, not according to Mishpat.
2)
What do we learn from "Ish li'Zero'o [Hayu Vach]"?
1.
Rashi: Whoever is stronger, he overpowers.
2.
Radak: Every man, according to his strength, wealth or [powerful] relatives, did evil and murdered. The same applies to "Ish Zero'a Lo ha'Aretz" (Iyov 22:8).