When he already pleaded guilty and was convicted?
WASHINGTON (AP) — Justice Department is dropping criminal case against ex-Trump adviser Flynn, according to court filing obtained by AP.
— Zeke Miller (@ZekeJMiller) May 7, 2020
Oh, this is FUCKED up.
— Grant Stern (@grantstern) May 7, 2020
How the hell can Bill Barr drop charges against someone who already pled guilty TWICE in open court?
Michael Flynn was the head of the Defense Intelligence Agency and betrayed his country to foreign powers.
This is EVIL. https://t.co/Hbxq22CGSp
Michael Flynn was a member in good standing of the ruling clique, and in mafia states, like the one Trump and Barr are building, one of the privileges of such membership is impunity for committing crimes on behalf of the boss. https://t.co/0s4kh8vy9w pic.twitter.com/yupPmuqP45
— Adam Serwer 🍝 (@AdamSerwer) May 7, 2020

Fruit of the poison tree.
Whether the judge goes for that reasoning is yet to be determined.