Lawyers in a court case aren't running around like the FBI and ATF. All those departments have separate functions.
Really, you still don't understand that the FBI and ATF are investigative arms of the DOJ. Damn your slow.
function - definition of function by the Free Online Dictionary, Thesaurus and Encyclopedia.
This is THE stated function of the DOJ and all it's agencies also know as their mission statement, ya see the part I put in bold?
To enforce the law and defend the interests of the United States according to the law; to ensure public safety against threats foreign and domestic; to provide federal leadership in preventing and controlling crime; to seek just punishment for those guilty of unlawful behavior; and to ensure fair and impartial administration of justice for all Americans.
USDOJ: About DOJ
One function, to argue otherwise would be like saying the motor in your vacuum cleaner or its wheels, has a function other than to aid you in cleaning the floor.