Good. Prosecuters should not be allowed to persuade the jury with anything but the evidence.
I’m an attorney, and have prosecuted state administrative cases.
Any sensible jury would easily have inferred that in a capital case the witness was taking a risk by coming forward; they didn’t need the prosecutor to make any obvious statements about it. I think the prosecutor pushed it too far - now I hope that a murderer isn’t free because of it.
In my own uneducated opinion, they need to do another trial.