You can't be serious - Kalifornia does not have the lowest murder rate.
Actually California has a pretty large evangelical community (I used to live there). It is far from being the most irreligious state. I looked at the top 5 for murder rate and religious ranking. California is somewhere below top five in either category. Murder rate is 4.8. Ranking in terms of being Christian (not the same thing but a different list - California is 33). Top 5 for Christian - Utah (1.9) (which is odd since they are not Christian), North Dakota (3.5) , Alabama (6.3), Louisiana (11.2), Oklahoma (5.5). Bottom 5 for Christian - Maine (2.0), Oregon (2.1), Alaska (4.0), Vermont (1.3), Washington (2.4).
What I found -
Salon.com lists the 8 countries that are most accomodating to atheists. Here they are by murder rate: Czech Rep - 1.7. Sweden - 1.0, Denmark - 0.9, Austria - 0.6, France - 1.1, Norway - 0.6, Australia - 1.0, Japan - 0.3 The U.S. rate is at 4.2. For states the most religious Mississippi - 8.0, Utah - 1.9, Alabama - 6.3, Louisiana - 11.2, Arkansas - 5.5. For the least religious states Vermont - 1.3, New Hampshire -1.3, Maine -2.0, Massachusetts - 2.8, Alaska - 4.0. Unless your religion is Mormonism it looks like a negative correlation to me between belief and murder (if a correlation does exist).