In the past month, criminals have murdered six police officers in the line of duty. The number might have been eight if not for the actions of two concealed handgun permit holders.Believe it or not, there were a lot more police murders a couple of decades ago. In the five years from 1990 to 1994, an average of 70 officers were killed annually. From 2010 to 2014, that number had fallen to 51 deaths per year. According to research by David Mustard at the University of Georgia, part of that drop occurred because states adopted concealed handgun laws. When states let law-abiding citizens carry concealed handguns, criminals actually become less likely to carry. Deterring criminals from carrying is of benefit both to civilians and to police.