The FBI has spent more than $3 million on unmanned aircraft from 2004 through May 2013, according to an audit released Thursday by the Inspector General.
The Department of Justice's law enforcement entities have spent $3.7 million on drones between four of its agencies, according to the report, though the FBI accounted for 80 percent of the amount. The Bureau of Alcohol, Tobacco, Firearms and Explosives had spent nearly $600,000 on drones to use in future operations.
The FBI told the Inspector General's Office they did not believe there was any difference between collecting evidence through a drone or a manned aircraft.
However, the audit described the FBI's drone use as "uncoordinated." Extended drone flights could track an individual's movements for hours and such pervasive surveillance could have legal ramifications if the tracking crossed over into private property, according to the Inspector General.
During a Senate Judiciary Committee hearing in June, then-FBI director Robert Mueller admitted the FBI had been using drones on U.S. soil in isolated instances that warranted specialized surveillance.
"Our footprint is very small," said Mueller. "We have very few and limited use and are exploring not only the use but also the necessary guidelines for that use."
Guidelines for drone use are particularly loose. The Federal Aviation Administration's 2012 Modernization and Reform Act will not require drone integration into the national airspace system until Sept. 30, 2015.
Both the Drug Enforcement Agency and the United Marshals Service have tested unmanned aircraft but have no plans to use them operationally. The USMS has spent $75,000 on drones, while the DEA acquired them from another federal agency at no cost, according to the audit.
Furthermore, the Justice Department awarded $1.2 million to fund drone testing for seven local law enforcement agencies and non-profit organizations.
The Justice Department's watchdog recommended forming a working group to differentiate drone capabilities from those of manned aircraft and address policy concerns shared among various federal agencies.
"No agency, including the FBI, should deploy surveillance drones without first having strong privacy guidelines in place," Jay Stanley, senior policy analyst for the American Civil Liberties Union's Speech, Privacy and Technology Project said in a statement.
Legislators have been trying to get Congress to tighten regulations on drone use. Reps. Zoe Lofgren, D-Calif., and Ted Poe, R-Texas, introduced the Preserving American Privacy Act in February that would require warrants for drone operations in private areas. Under the proposed law, law enforcement agencies would need a court order and provide public notice before deploying drones to collect information in public space.
American support for drones is lukewarm at best. An August Monmouth University poll suggested three in four Americans want law enforcement agencies to obtain a warrant before using drones, while 69 percent said their privacy would be threatened. However, 83 percent of respondents favored drones in search and rescue missions and 62 percent favored drone use for border patrol.
Numerous states have introduced laws to combat their concerns at a local level. Virginia became the first state to issue a statewide limitation on drone use when Gov. Bob McDonnell authorized a two-year moratorium in April.
Laws in Florida, Idaho and Tennessee require law enforcement agencies to obtain a warrant before using drones. In Montana, evidence obtained through drone use is only permissible if it was obtained under a warrant.