There is an additional wrinkle here. The overwhelming majority of people prosecuted by the Feds are guilty of something (and not just of some "made up" crime). I worked for a federal appellate judge. Saw dozens of criminal cases come up on appeal. Didn't see a single one from the Feds where the evidence of guilt wasn't overwhelming (even if some convictions were defective for technical reasons, and even if some were for debatably immoral conduct like drug trafficking). They don't go around baiting random people they think are innocent to lie in an interview. They do it to make sure they have concrete points of leverage to get information about the rest of the crimes.
Of course, this really sucks if you're innocent (though even then, often your associates aren't and you were in the wrong place at the wrong time). When these guys see guilty people lie to their face day in and day out, it's hard to give the rare actually innocent person the benefit of the doubt. They have the moral obligation to do that, mind you. It's just understandably hard.
It's not what he was charged with, it's the evil and horrid behavior of Carmen M. Ortiz, the U.S. attorney for Massachusetts, after being charged that disgusts most people.
Of course, this really sucks if you're innocent (though even then, often your associates aren't and you were in the wrong place at the wrong time). When these guys see guilty people lie to their face day in and day out, it's hard to give the rare actually innocent person the benefit of the doubt. They have the moral obligation to do that, mind you. It's just understandably hard.