<span style="color: #222222;">In United States, at least six people including a Pennsylvania state trooper were killed and dozens injured in a string of weekend violence and mass shootings.<br />''<br />'' According to a Professor of Public Policy and statistics at Carnegie Mellon University Daniel Nagin, there's no question there's been a spike in violence, theories include the possibility that violence is driven by the prevalence of guns in America, or by less aggressive police tactics or a decline in prosecutions for misdemeanor weapon offenses.</span><br />