You are flatly wrong. Please stop posting misinformation.

"The USA [US Attorney] is invested by statute and delegation from the Attorney General with the broadest discretion in the exercise of such authority."

http://www.justice.gov/usao/eousa/foia_reading_room/usam/tit...

  The United States Attorney, within his/her district, has 
  plenary authority with regard to federal criminal matters. 
  This authority is exercised under the supervision and 
  direction of the Attorney General and his/her delegates.

  The statutory duty to prosecute for all offenses against 
  the United States (28 U.S.C. § 547) carries with it the 
  authority necessary to perform this duty. The USA is 
  invested by statute and delegation from the Attorney 
  General with the broadest discretion in the exercise of 
  such authority.

  The authority, discretionary power, and responsibilities of 
  the United States Attorney with relation to criminal 
  matters encompass without limitation by enumeration the 
  following:

  Investigating suspected or alleged offenses against the 
  United States, see USAM 9-2.010;

  Causing investigations to be conducted by the appropriate 
  federal law enforcement agencies, see USAM 9-2.010;

  Declining prosecution, see USAM 9-2.020;

  Authorizing prosecution, see USAM 9-2.030;

  Determining the manner of prosecuting and deciding trial 
  related questions;

  Recommending whether to appeal or not to appeal from an 
  adverse ruling or decision, see USAM 9-2.170;

  Dismissing prosecutions, see USAM 9-2.050; and

  Handling civil matters related thereto which are under the 
  supervision of the Criminal Division.