Researchers at Stanford have concluded that, contrary to the political commonplace that right-to-carry (RTC) or concealed-carry laws decrease violent crime, such laws have actually increased the number of violent crimes in the states that have passed them since 1999.
study: http://news.stanford.edu/news/2014/november/donohue-guns-study-111414.html
http://www.rawstory.com/rs/2014/11/more-guns-more-crime-stanford-research-undermines-the-nras-favorite-study/