One area where the numbers are a little murkier is ambush attacks like the Dallas shooting, where killing police officers is the sole intent of the crime. These are generally very rare, with the number of officers dying in these attacks each year in the single or double digits. But they have become slightly more common: during George H.W. Bush's administration (the first administration for which the FBI provides complete data) roughly eight officers died in ambush attacks each year. That rose to nine under Clinton, and 10 per year under George W. Bush and Obama (through 2014).