States that implemented "shall-issue" concealed carry laws reduced murders by 8.5%, rapes by 5%, aggravated assaults by 7%, and robbery by 3%, according to a 2000 analysis of FBI crime data by economist and political commentator John R. Lott Jr., PhD. Lott calculated that 1,570 murders, 4,177 rapes, 60,000 aggravated assaults, and 12,000 robberies could have been prevented between 1977 and 1992 if concealed carry had been legal in every US state during that time period.  In addition, a 2013 peer-reviewed study in Applied Economic Letters, found that between 1980 and 2009, "states with more restrictive CCW [carrying concealed weapons] laws had gun-related murder rates that were 10% higher."  Detroit Chief of Police Larry Craig said permitted concealed weapons are "a deterrent," and "Good Americans with CPLs [concealed permit licenses] translates into crime reduction."  A 2013 survey of 15,000 current and retired police officers found that 91.3% support the concealed carry of guns by civilians. Concealed Guns ProCon.orgCarrying a concealed handgun could help stop a public shooting spree. After the Apr. 20, 1999 Columbine High School massacre, the state of Colorado enacted the 2003 Concealed Carry Act to allow law-abiding citizens the right to carry a concealed weapon. The CATO Institute concluded that this law helped to stop a massacre at the New Life megachurch in Dec. 2007 when a volunteer security guard for the church who was carrying a concealed handgun shot an attacker who had opened fire in the church.  According to John R. Lott Jr., PhD, "when states passed concealed carry laws during the 19 years we studied (1977 to 1995), the number of multiple-victim public shootings declined by 84%. Deaths from these shootings plummeted on average by 90%, injuries by 82%."