This is stated in Gus Russo's "The Outfit", while there is some suspicion that guys like Humphreys, Giancana, Accardo & Battaglia fed the IRS agents info to get rid of Capone. There isn't much to support the claim. Also, Russo points out that Humphrey's & Guzik actually tried and managed to fix the jury for Capone, and it worked, they got to some of the jurors. Problem was, the judge and prosecutors found this out right before the case began and on a whim, switched juries at the beginning of the trial. Which angered Capone and the rest of the guys, especially Humphrey's, because that wasn't an easy job to get to THOSE jurors, as they were sequestered. And he felt it was all for nothing, his work that is.