When John F. Kennedy was assassinated in 1963, the Zapruder film provided investigators with key evidence of the shooting. Fifty years later, crime scene investigation has evolved into a complex science, and now, with smartphones, and other mobile devices, video footage of events is readily available to assist investigators in solving crimes.
The Federal Bureau of Investigations is our federal police force, “to protect and defend the United States against terrorist and foreign intelligence threats and to enforce the criminal laws of the United States." However, in that mission the FBI has investigated its own citizens, even it's own presidents. Pulitzer prize winning author Tim Weiner discusses the complicated history of the FBI.