Diplomatic immunity is not intended to help murders go free, but it has been used to do that. There are a good reasons for diplomatic immunity, as it helps to protect people who are diplomats in foriegn nations, but in the modern world that is rarely neccesary and it has become abused.
Diplomatic immunity should be limited to non-violent and minor offenses. With more international acts of terrorism occurring in the world and increased tension among countries, there should be more emphasis placed on proper respect for the customs and laws of countries by diplomats and their family members who are visitors.
Yes, there should be a limit to diplomatic immunity so that innocent people do not get hurt. People should not be able to use diplomatic immunity in instances in which they harm others for no reason. Diplomatic immunity should not be used in any instance in which someone was injured that severely.
Victims of violent crimes are entitled to justice, and prosecution should occur regardless of status. Providing diplomatic immunity to perpetrators of violent crimes is absurd, and the current policies need revision. When a person has no fear of the judicial system, it can escalate criminal behavior. This is a danger to the general public.