The lead agency for terrorism and counterintelligence law enforcement is the FBI , although a number of units of the Department of Homeland Security may provide support After the Oklahoma City bombing of 19 April 1995 , by Timothy McVeigh , an American , the CI definition reasonably extends to include domestically-originated terrorism . There is also the challenge of what organizations , laws , and doctrines are relevant to protection against all sorts of terrorism in one 's own country . See Counter-intelligence Force Protection Source Operations for a discussion of special considerations of protection of government personnel and facilities , both in the US and internationally . Immigration services , which had been under the United States Immigration and Naturalization Service ( INS ) , were transferred from the Department of Justice to the Department of Homeland Security in March 2003
Oklahoma City bombing
Oklahoma City bombing
Counter-intelligence and counter-terrorism organizations