From the NYT 5-17-17 article:
As a special counsel, Mr. Mueller can choose whether to consult with or inform the Justice Department about his investigation. He is authorized to investigate “any links and/or coordination between the Russian government and individuals associated with the campaign of President Donald Trump,” according to Mr. Rosenstein’s order naming him to the post, as well as other matters that “may arise directly from the investigation.”
Congress cannot get the scope letter, so this must have been leaked. Of particular interest, is the second statement regarding 'other matters".
Hmmmm