Most likely you will be excluded from hearing the witnesses testifying in the criminal case. In Texas criminal cases attorneys (both the prosecutors and defense attorneys) will invoke “the rule”. The rule excludes all witnesses from hearing the case because the witnesses if they hear each others testimony will adjust their statements or what the witness will say before the jury. The “rule’s” goal is to help ensure the truth will be told to the jury that will render the verdict.
If either party, the prosecutor or defense, invokes the rule, the judge will order the witnesses present out of the courtroom and instruct them not to speak with each other for the remainder of the trial. In the event the witnesses are present in the courtroom and listen to trial testimony, talk to the other witnesses and discuss their testimony given to the jury, or listen to other witnesses discuss their testimony yet to be given, the judge will exclude the witnesses from testifying. In rare circumstances judges have notified the jury of instances of witnesses have violated the court’s orders and ordered the jury to strike or disregard the witnesses’ testimony that violated the court’s order. The court takes very seriously the violations to the “rule” because is strikes at the main effort of the trial to secure the truth, and attempts to avoid the prosecution or the defense “tampering” with witness testimony and what they will testify to during the trial. In rarer circumstances it could cause a mistrial; if a government witness causes the mistrial it could bar further prosecution because double jeopardy attached in the criminal case. In any event, if a jury is informed about the misconduct it will hurt one side or the other depending who is testified and violated the rule.
If the person is to be a fact witness or a character witness during the trial, it is normal for attorneys to tell the witnesses in advance to expect to be excluded from the trial, and not hear other witnesses testifying before the jury or judge. Attorneys will tell the witnesses not to discuss their testimony with anyone else because the more the witness discusses their testimony with others especially others involved in the case, they (the other people you discuss your testimony or information about the case) could be used as an impeachment witness. The impeachment witnesses could then be called to testify about your conversation with them and your inconsistent statement be told the jury; thereby, making you out to be liar.
Should you have any questions about you being excluded from the trial and not listening to the trial testimony, ask the attorney who is instructing you — you could be crucial to the case.
If either the State or the defense invokes what is called The Rule, then all potential witnesses, including character witnesses, must remain outside the courtroom or their testimony can be excluded from the trial. However, the lawyer can ask that after the witnesses testify that they be excused from the rule so they can remain in the courtroom to hear the following witnesses and certainly so they can hear the final arguments of counsel.
I find that it is helpful simply to have people at the courthouse supporting clients emotionally as well as demonstrating that they are willing to take the time out of the day and/or work to come to court. The jurors see this, too. This kind of support is very helpful for the accused.