Oli, I'm a scholar of the Rosenberg spy case, one of the worst examples of government persecution of innocent people, aided and abetted by incompetence of their counsel. In one example:

The FBI waited until the middle of their trial to arrest William Perl, a college classmate of Rosenberg's, and charged him with being a member of the so-called "Rosenberg spy ring." Perl had earlier come to the FBI to report that someone had offered him $2k to leave the US following Rosenberg's arrest. The prosecutor, Irving Saypol, announced to the media that he would call Perl as a prosecution witness in the Rosenberg trial. He never did: the FBI freed Perl a few days later because evidence was insufficient to bring him before a grand jury.

After the Rosenbergs' conviction, their lawyer, Emanuel Bloch, asked an appellate court to overturn the verdict because Saypol's statement was front-page news and the jury wasn't sequestered, probably prejudicing the jury. The appellate court found that Saypol's "behavior was wholly reprehensible," but they didn't order a new trial because Bloch had failed to move for a mistrial after Saypol made his statement to the media.