Allegations of misconduct, termination, and even criminality, would not render the officer incompetent as to testify. Evidence of any misconduct by the officer, to the extent that it can be used at all, would go the credibility and weight of her testimony, not to its admissibility. I see tricky evidentiary questions at the trial of this case, as your attorney tries to get in as much evidence of the officer's problems as possible, and the prosecutor tries to keep it out. It should be an interesting trial.
The prosecutor can subpoena any witness to testify at trial, especially a fact witness like you describe. Your PD may or may not be able to cross-examine the officer about the facts you describe. It will be up to the judge to allow or restrict these type of questions on cross if objected to by the prosecutor.
I am trying to give you a general answer to your question. We do not have an attorney-client relationship by this response on the avvo website. I have not been retained to represent you. I am licensed to practice law in Kentucky and in federal court in this state and the Southern District of Indiana. You need to seek legal advice from an attorney licensed to practice in your area..
I see you are in Little Rock. If it's Officer Sims, I would really doubt prosecutor is going to go through with it. If there were other arresting officers, the prosecutor might.
We are expressly not creating an attorney client privilege. While I am a criminal defense attorney, I am just speaking in general about the law in Arkansas and not your specific situation. I am not providing advice, I am just assessing a situation. If you are facing charges then you need to consult a professional.