The FBI often works in conjunction with other federal agencies , including the U.S. Coast Guard ( USCG ) and U.S. Customs and Border Protection ( CBP ) in seaport and airport security , and the National Transportation Safety Board in investigating airplane crashes and other critical incidents . Immigration and Customs Enforcement ’s Homeland Security Investigations ( HSI ) has nearly the same amount of investigative manpower as the FBI , and investigates the largest range of crimes . In the wake of the September 11 attacks , then – Attorney General Ashcroft assigned the FBI as the designated lead organization in terrorism investigations after the creation of the U.S. Department of Homeland Security . HSI and the FBI are both integral members of the Joint Terrorism Task Force
September 11 attacks
September 11 attacks
Federal Bureau of Investigation