¶1When the People rested, there was a discussion with the court as to whether the defendant (because of his criminal record) would testify on his own behalf. After the prosecutor refused the court’s suggestion to forego such questioning, the court, in a Sandoval ruling, stated that the People could inquire only as to whether the defendant had been convicted of robbery; the court specifically precluded inquiry upon whether the robbery had been "armed” or upon any of the other underlying circumstances. After consultation with his attorney and in view of the court’s ruling, the defendant testified, acknowledging the robbery conviction on direct examination. On cross-examination the prosecutor asked the following question: "Q. By the way, you told the defense lawyer you were convicted of the felony of robbery. Were you guilty?” Over objection, the court allowed the question.
"A. I pleaded guilty.
"Q. Don’t play games with us.
"me. auerbach: Objection to the form.
"the court: Disregard that remark.
"Q. Were you guilty? Did you do it?
"A. I was told in Westchester County in 1981 if I didn’t accept three to six for a robbery, then I would get six to twelve. So I pleaded guilty in Westchester County.
"Q. Were you guilty in that robbery?
"A. No, I wasn’t. I pleaded guilty to that robbery.
*189"Q. You were innocent of the robbery you pleaded to, and you got three to six years?
"A. Three to six years—an illegal sentence.
"Q. Excuse me—of what?
"A. Nothing.”
¶2At the next sidebar the prosecutor, claiming that the defendant had "opened the door”, informed the court that he intended to go into the underlying facts of the robbery. A robing room conference followed from which the court excluded the defendant. While the court, after argument, stated that it was the prosecutor who "opened the door” and that the prosecutor could not "set the defendant up” with questions as to his guilt and "take advantage of [defendant’s] answer”, the court’s amended Sandoval ruling nevertheless permitted the very inquiry for which the defendant had, to use the court’s expression, been "set up”. The court stated:
¶3"If he is a predicate felon, you can ask, because he opened the door when he said that was an illegal sentence … You could ask him was he arrested right after the robbery, how long after the robbery was he arrested …
¶4"You can ask him … is he familiar with this particular location, when he was arrested, under what circumstances he was arrested.”
¶5Defense counsel objected that this last ruling ranged well beyond the original Sandoval determination and that the prosecutor would now benefit by dint of having violated that determination, but the court held to its more recent ruling, observing that cross-examination on the circumstances of the arrest was relevant to the issue of credibility. Questioning resumed as to the prior conviction and the prosecutor elicited that the defendant had been arrested in Yonkers after a car chase through the Bronx.
¶6The prosecutor then went into the facts of a prior plea negotiation had before a different Judge:
"Q. Isn’t it a fact that you killed Alton Jarvis, then your gun jammed and you gave it to Reggie Green and told to him to get rid of the gun?
"A. No.
"Q. Do you know Reggie Green? …
"A. I know a couple of Greens …
"Q. Did you ever tell anybody that Reggie Green ended up with the murder weapon?
"A. I think I told the judge that and the District Attorney.
*190"mr. karen: I have no further questions.
"the court: I am sorry, what was the answer?
"the witness: I think I told the judge and the District Attorney.
"the court: When you say the judge, which judge were you referring to?
"the witness: The Judge before yourself.
"mr. karen: I have no further questions”.
The foregoing was made a part of the prosecutor’s summation:
"This man, Dickerson, tells us he doesn’t know anything about the crime, and initially said he never saw a gun, doesn’t know a Reggie Green. He tells some other Judge on this case Reggie Green ended up with the murder weapon.
"What stronger proof could you have than the defendant’s word?”
¶7A Sandoval hearing is a material stage of the trial which requires the presence of the defendant. As the Court of Appeals observed in People v Dokes (79 NY2d 656, 660), the presence of the defendant is essential since a Sandoval hearing involves "factual matters about which defendant might have peculiar knowledge that would be useful in advancing the defendant’s or countering the People’s position.” At the reopened Sandoval hearing the defendant, over objection, was denied this statutorily guaranteed due process right to meaningfully participate at the hearing in the robing room (see, People v Gebrosky, 80 NY2d 995). Defendant was excluded from a hearing the purpose of which was to decide whether the prosecutor could question him about the facts of his robbery conviction. As the resulting ruling was obviously unfavorable to defendant, harmless error review is not appropriate and the defendant is entitled to a new trial (People v Favor, 82 NY2d 254).
¶8Further, the record is clear that the defendant testified with the understanding that the Sandoval ruling allowed but a single question as to whether or not he had been convicted of robbery. The purpose of the Sandoval ruling, of course, is to let the defendant make an informed decision as to whether he will testify in his own behalf (see, e.g., People v Astado, 131 AD2d 684, 685). Plainly the purpose of the ruling in the present case was undone when the prosecutor with the court’s acquiescence went beyond the limitation relied upon by the defendant when he took the witness stand. It was moreover not the defendant, but the prosecutor who "opened the door”, *191and the court’s appropriate role at that juncture was not to open the door wider but to shut it in adherence to the ruling already made. Undoubtedly, the defendant’s credibility was in issue and in that context particularly the court’s error denied the defendant a fair trial.
¶9Reversible error was also committed when the prosecutor was allowed to question the defendant on the substance of a plea negotiation before another Judge. Plea negotiations should be open and frank and unless there is an agreement with the prosecutor to allow the use of these discussions, such give and take before a Judge must remain out of a future trial. (See, People v Spitaleri, 9 NY2d 168.) The prosecutor’s breach of this rule in this case where statements from plea negotiations were used in both cross-examination and summation was highly prejudicial.
¶101 would reverse and remand for a new trial.