If The President Doesn't Make Decisions On Prosecutions, Who Does?

Robert Gibbs made this curious statement on Meet the Press, according to Fox News:

"The president doesn't open or close the door on criminal prosecutions of anybody in this country, because the legal determination of who knowingly breaks the law in any instance is one not made by the president of the United States," he said on NBC's "Meet the Press."

What could this statement mean? Taken at face value, it is true that "the legal determination of who knowingly breaks the law" is made by the trier of fact--either a judge or jury. But this is true of any prosecution. It would be nonsensical to say that a district attorney does not make decision on who to prosecute, since he or she does not make the ultimate determination of guilt.

Instead, it seems like Gibbs is doing some buck-passing on behalf of his boss. That is, whatever happens, it's going to be either because Congress, or Holder, or the slimy custard man made the call. But the Constitution does not vest the authority to execute the law in a congressional sub-committee or an appointed executive official. It vests in the president.