Let me explain why.
After all the evidence has been presented and all the testimony has been heard, the attorneys will then make their closing arguments. After each side has made closing arguments explaining why their client should get a verdict in their favor, the trial judge will then have the court officer lock the courtroom door.
No, it's not to prevent jurors from escaping.
Rather, it's to prevent people from coming into the courtroom and disrupting the judge's legal instructions to the jury.
If you happen to be walking by a courtroom where the judge is giving the jury legal instructions, there will be a sign on the door that says "JUDGE CHARGING JURY. DO NOT ENTER."
The judge wants the jury paying close attention.
He doesn't want them focusing on who is coming into or out of the courtroom.
The judge will typically spend 45 minutes to an hour going through in explicit detail the legal instructions that apply to your case.
Do the attorneys know which legal instructions the judge will give to the jury?
Does the judge decide on his own which instructions to give or does he accept input from the attorneys?
The answer is yes and yes.
You see, a few days before your trial approaching the end, the judge will require the attorneys to appear for a conference with the judge to discuss those legal instructions he plans on giving the jury. This is known as a charge conference.
Each attorney will already have prepared a set of legal instructions favorable to their side and given a copy to the judge or his law clerk. We typically title this "Proposed Legal Instructions."
The judge will ask us why we have requested certain sections of law and whether we are asking for any legal instructions to be modified to reflect your specific facts. We now have to convince the judge why the section of law we are asking for is relevant and important. The defense will chime in and usually oppose our requests.
Likewise, the defense will be given an opportunity to ask for jury instructions and modified instructions favorable to the defense. We typically will oppose the defense's requests. The judge will then rule on which specific legal instructions he will be explaining to the jury.
Then we will make a record with the court stenographer present to explain which instructions he will be giving to the jury and which ones he did not accept from us and my opponent. The attorneys then get to make our objections known 'on the record' to preserve in the event one of us needs to appeal the verdict.
If I feel that the judge is planning on discussing the law with the jury that is favorable to the defense, can I ask for a mistrial? The reality is that I can always ask, but I need a good faith basis to do so. If I don't have a good faith reason to ask for a mistrial, not only will the judge deny my request, but often the judge will express his frustration and not appreciate my request.
If the judge chooses legal instructions favorable to my opponent, that is NOT grounds for a mistrial. Instead, it may ultimately be grounds for an appeal and maybe a reversal of a jury verdict, but not a mistrial.
A mistrial is requested when something really bad has happened that has now prejudiced the jury.
Maybe an attorney asked a witness a question that was deemed to be off limits by the judge.
Maybe a piece of evidence was introduced and now the jury cannot 'unsee' it leading to obvious prejudice to one side.
There could be many reasons why an attorney asks for a mistrial.
If the judge grants a mistrial, it means that all of our efforts, all of the courts' efforts to prosecute your case are now out the window and wasted. The jury will be excused and the attorneys will be directed to start your trial all over again from the very beginning by picking a new jury.