Prof. Colin Miller has an interesting post about prosecutorial discretion during the course of trial.
Besides getting a conviction and an appropriate sentence, a secondary gain of the prosecutor is to have the case affirmed on appeal. Affirmance means a guilty person doesn’t walk or get a new trial.
In the post Prof. Miller refers to a successful prosecution objection excluding “compelling defense evidence,” on what he terms a technicality. He closes his post:
Absent some argument that the cell phone records are inaccurate, I have trouble understanding the prosecutor’s thinking in keeping them from the jury. Even if the prosecutor was convinced of the defendant’s guilt (as the story reports), a conviction obtained in what appears to be a close case, without letting the jury hear this compelling evidence, seems sure to be a pyrrhic victory. Putting aside any ethical considerations, the conviction (as described in the story) appears to be either the product of trial court error (if the cell phone evidence was properly offered) or ineffective assistance of counsel (if it was not). A prosecutor who keeps out such evidence (in close cases) is playing with fire — effectively providing the defendant with a free chance at an acquittal, due to the strong likelihood of reversal on appeal, and courting a best case scenario of a temporary conviction, followed by the significant costs (financial and otherwise) of a retrial where the jury will ultimately hear the cellphone evidence.