Murder in the Torah is punished by the death penalty, but with many conditions.
Were the rules of death penalty the same for Jews and non-Jews living in the holy land? What were the differences?
Was the Sanhedrin able to judge non Jews?
There are two laws in the 7 noahide laws which pertain to this. The first being not to mirder and the second to establish courts of justice. The court systems would set up procedures of how to deal with witnesses and how the offender should be punished.