From today's Tribune article (linked above):
Rezko's request comes as he restarts talks with federal prosecutors. Those talks hit a stumbling block as Rezko asked to be let out of solitary confinement at the downtown federal lockup. He asked for a rushed sentencing in January. But last week's revelation that the government has recordings in the governor's case, appeared to change Rezko's mind about cooperating.
What could Rezko know now that he didn't know before? Is he going to change his past statements that Fitz said were inconsistent in significant ways with those of other witnesses? I'd say probably. If he tightens Fitz' case against Blagojevich (or helps make a case against others suspected of doing bad deeds with Blagojevich) he's likely to get a better sentencing cut recommendation from the Government.
As Sir Walter Scott famously wrote, "Oh what a tangled web we weave, When first we practise to deceive!" But, which version of Rezko's "truth" is real, the first one or the one he now wants to tell to match the one Fitzgerald wants to hear?
Cooperator testimony is purchased testimony, purchased by the Government with promises of leniency. Freedom is a commodity far more precious than money. It is inherently untrustworthy.