He can do it at the preliminary hearing. If it is done there, then the prosecutor can refile the charges by going to the grand jury, but if the judge dismisses the charges after the trial has started, then the prosecution cannot re-file.
This may be a tactic to pass the buck to the presiding judge and let him dismiss the charges. Then the prosecutor can take it to the grand jury who will also dismiss the charges. Then I believe it is "game over". It is interesting to note that Corey decided to forego the Grand Jury and instead bring charges under an information and then force the matter to a preliminary hearing. I think she knows she has no case but she wants to pretend she does and then go to the prelim where the charges will be dismissed and then go to the grand jury, where the same charges will be dismissed.
I have trouble believing that she is so stupid as to not know that she doesn't have a prayer for a murder conviction on the information she has filed. But then she is a government employee.
The preliminary hearing is at the end of May?