Vouching. Don't do it. It'll get you reversed. And, as an aside, it's also fundamentally unfair.
Like here. Here are the first words out of the prosecutor's mouth to begin her rebuttal closing argument:
“I have a duty and I have taken an oath as a deputy District Attorney not to prosecute a case if I have any doubt that that crime occurred. [¶] The defendant charged is the person who did it.”
That's vouching. It's improper. And, indeed, it got the conviction reversed.
I can understand why the prosecutor said what she did. Or, more accurately, why she thought that it might be okay to say what she did. But she was wrong. Plus, even purely as a tactical matter, the benefits of vouching -- even in a case where you think it might be okay -- are rarely worth the risk of a reversal. So don't do it. And, again, it's also wrong. Convict on the merits. Don't try to convict by getting the jury to take your words for it. Play tough, but also play fair.
That said, while I understand that Business and Professions Code 6086.7 requires that the opinion be referred to the State Bar since the conviction was reversed for prosecutorial misconduct, I also hope -- and very much think -- that the prosecutor won't get in disciplinary trouble for what she did. She made a mistake; indeed, an error of judgment. But she didn't do something worthy of further sanction. At least in my mind.
One final point. Justice Rothschild -- in the majority -- clearly wins the debate with Justice Vogel (in dissent)regarding whether the error was prejudicial. Indeed, in all honesty, I'm frankly stunned -- and yet, ironically, simultaneously not entirely surprised -- by Justice Vogel's view. Justice Vogel thinks there was no prejudice because there was a single eyewitness who testified that he was sure the defendant was the guy. But wholly apart from the many, many reasons elicited at trial why the eyewitness might not be believed (and there's so much on that issue here), to say that the testimony of a single eyewitness allows us to be confident that the defendant did it -- and hence that the jury would have convicted anyway -- so flatly conflicts with all of the modern research and analysis regarding the flaws of eyewitness identifications that I really wonder what Justice Vogel could possibly be thinking. To hear a judge essentially conclude "Oh, well, he was identified by an eyewitness, so we're sure he did it, even though there's no other evidence at all against him" in the modern era is pretty surprising. And yet, sadly, perhaps not surprising at all.
Old habits -- and beliefs -- assuredly die hard.