He already has the goods on lots of folks so when/if they are so foolish as to lie he has them by the yinyang. If they lie they do so at great risk. He probably has all the evidence he needs to indict everyone already but he wants to include as many wrongdoers as he can so he investigates/questions/makes notes and those who lie? My oh my. Those who take the 5th because they are guilty? Another my oh my. Mueller holds ALL the cards. He owns the game. The players are just there because they participated in a grand scheme/great con and now are paying the piper for it. What comes next? Whatever it is will be supercalifraglisticexpialidocious! With or without a spoonful of sugar! :)