My question is, if this is the worst misconduct he has seen in the last 25 years then why did he not do anything about it during the trial? Sanctions, dismiss charges, etc.
During the post-trial process, even more wrongdoings were discovered at which point he demanded that Mukasey personally respond to the issues. Mukasey ducked and left office without a response. Holder inherited it and removed the whole team of prosecutors in February, assigning a new bunch of attorneys to take a new look at the situation. Those attorneys found yet more evidence favoring Stevens that had been withheld and resulted in the recommendation for dismissal.
In retrospect, I think Sullivan wishes he threw the whole case out earlier. But no single event during the trial seemed to warrant it at that time, in his view, anyway. When evidence came up after trial, there was no action he could take that could undo the damage done during testimony.