Law enforcement in the United States is primarily the responsibility of local police and sheriff's departments, with state police providing broader services. Federal agencies such as the Federal Bureau of Investigation (FBI) and the U.S. Marshals Service have specialized duties. At the federal level and in almost every state, jurisprudence operates on a common law system. State courts conduct most criminal trials; federal courts handle certain designated crimes as well as appeals from state systems.Among developed nations, the United States has above-average levels of violent crime and particularly high levels of gun violence and homicide. Some scholars have associated the high rate of homicide with the country's high rates of gun ownership, in turn associated with U.S. gun laws which are very permissive compared to those of other developed countries.