evidence: According to a 2017 Harvard Business School review, waiting period laws that delay the purchase of firearms by a few days reduce gun homicides by roughly 17%. But Sam Paredes, executive director of Gun Owners of California, called waiting periods "an ineffective policy to try to affect gun crime." [...] Daniel Webster, co-director of the Center for Gun Violence Solutions at Johns Hopkins’ Bloomberg School of Public Health, said waiting periods are important, and it’s obvious to him why more states don’t require them: Many firearm laws, he said, are "written by people who sell guns." [...] Hawaii has the longest waiting period in the U.S., at 14 days. Alan Beck, an attorney representing residents who are challenging various aspects of the state’s gun laws, said the two-week period seems arbitrary. If it’s meant as a cooling off period for someone who is angry, he said it won’t have an effect on potential gun buyers if they already own a firearm.