The FBI has spent more than $3 million on drones, while the Bureau of Alcohol, Tobacco, Firearms and Explosives has spent almost $600,000 and plans to use drones for future missions, the IG report says.
DOJ has spent $1.26 million on drones for police departments across the country.
One local law enforcement agency estimated the costs of drone use at $25 per hour for one unit, compared to $650 per hour for a manned aircraft.
According to the report, the drones used by the Justice Department weigh up to 55 pounds.
The IG report suggests the creation of a DOJ working group to determine whether drones require their own legal policies.