Positive Mitzvah 225
Exiling a Person to a Refuge City
Numbers 35:25 "And he shall live there until the death of the high priest"
A person who accidentally caused the death of someone else must flee to a refuge city (See Positive Mitzvah 182). He must stay in the refuge city until the death of the High Priest.
Negative Mitzvah 295
It is forbidden to accept a ransom from a murderer who killed intentionally
Numbers 35:31 "You shall take no ransom for the life of a murderer who is guilty of death"
We are forbidden to allow a convicted murderer to pay money so that he will not be executed. We must see that the Torah Law is applied and that he receives his due punishment.
Negative Mitzvah 292
It is forbidden to execute a person before he stands trial
Numbers 35:12 "The murderer shall not die until he stands before the congregation in judgment"
We are forbidden to execute a person whom we saw committing a crime until he is brought to trial.
Even if we know that he will be sentenced to death, we must leave the judgment and penalty up to the court.