From Reason:

California has the gun laws that restrictionists say they want. Universal background checks? Yes, indeed. “Assault weapon” ban? Through tighter and tighter iterations, you bet. Registration? Uh huh. Red flag law to strip guns from the hands of maybe, potentially dangerous people? For several years now, and toughened just last month.
These are dream laws for anti-gunners around the country, and yet they didn’t stop Nathaniel Berhow from murdering two people and injuring three others before shooting himself at Saugus High School in Santa Clarita, California, earlier this month. Instead of being stymied by legal restrictions, the killer worked around them.