This is, by the way, a serious question.
Article 1 section 1 says
"All legislative Powers herin granted shall be vested in a Congress Of the United States, which shall consist of a Senate and House of Representatives
Article 1 Section 7 says
"Every Bill which shall be passed the House of Representatives and the Senate shall before it becomes a law, , be presented to the President of the United States; If he approve he shall sign it, but if not he shall return it, with his objections to the House in which it shall have originated.
Article 1 Section 8 says
"Congress shall have power to make all laws which shall be necessary and proper for carrying into Execution the forgoing Powers, and all other powers vested by this Constitution in the Government of the United States in any Department o Officer thereof
Article 2 Sec 1 says
"Before he enter on the Execution of his Office, he shall take the following oath of Affirmation: "I do solemnly swear (or affirm) that I will faithfully execute the Office of the President of the United States, and will to the best of my Ability, preserve, protect and defend the Constitution of the Unites States.
Article 3 Sec.2 says
"In all cases affecting Ambassadors, other public Ministers and Consuls and those in which a State shall be a party, the supreme Court shall have original jurisdiction. In all the other cases before mentioned, the supreme Court shall have appelate Jurisdiction, both as to Law and Fact, with such exceptions, and under such regulations as the Congress shall make."
So, Congress makes the laws and sends them to the President. If he does not like them he sends them back.
Congress can make laws to carry out the Execution of laws and anything they forgot and for execution of the laws for any Department or Officer.
Congress makes laws. The president takes an oath to faithfully execute the Office of the Presdient. The Surpeme Court reviews for facts
Now since Congress makes the laws, the President executes them, and the Supreme Court reviews them, how is Congress going to know what is "necessary and proper for carrying into Execution" with knowing whats going on? Hmmmm... it may have something to do with The House Government Reform and Overisight committie.
Now can you show me what in the Constitution supports your claim that Congress does not have an oversight role in criminal prosecutions?