When separate persons are jointly accused of the same offense of conspiracy, the court shall order, at the request of one of them, a separate trial if it is shown that any one of the other conspirators, after having carried out or failed in the objective for which the alleged conspiracy was planned, made declarations, admissions or confessions pertinent to the case which might adversely affect the person who requested the separate trial, unless the prosecution announces that he will not offer in evidence said declarations, admissions or confessions, nor shall he make any reference thereto during the trial.