As I was reading in the Book of Mormon today I came across two verses that accutely clarify how murderers and robbers should be dealth with. I found it to be very clear and yet incredibly profound.

3 Nephi 5:4-5

• 4 And now it came to pass that when they had taken all the robbers prisoners, insomuch that none did escape who were not slain, they did cast their prisoners into prison, and did cause the word of God to be preached unto them; and as many as would repent of their sins and enter into a covenant that they would murder no more were set at liberty.
• 5 But as many as there were who did not enter into a covenant, and who did still continue to have those secret murders in their hearts, yea, as many as were found breathing out threatenings against their brethren were condemned and punished according to the law.

This passage of scripture shows us that criminals should be given the opportunity to hear the gospel of Jesus Christ and to fully repent. Those who truly repent should be pardoned. Those who, after hearing the gospel, continue to have evil in their hearts and do not repent should be condemned to the full extent of the law according to their crimes.

That is very straight forward.