Why Wasn't The Juan Johnson Jury Told About His Cocaine Arrest Last Year???

The jury in Juan Johnson's civil trial was not told that just last year Johnson, as part of a federal sweep of a Chicago street gang, was arrested and charged with being involved in the sale of crack cocaine. Johnson was set to plead guilty to that offense in March of this year but somehow managed to convince the United State's Attorney's Office to postpone his guilty plea until after his civil trial. Johnson obviously did not want the jury to hear evidence that was inconsistent with his claimed testimony of living his life on the straight and narrow. And why did the United State's Attorney's Office AGREE to the postponement?? Here is a copy of the motion Johnson filed requesting the continuance. Johnson managed to keep his crack cocaine offense from the jury, but at the same time managed to introduce evidence that Detective Guevara allegedly (according to who?) had a reputation for framing criminal suspects. Hardly seems fair . . .
(Photo from LA Times Blog Post)