Yes, and no. Prior arrangements can be useful for your attorney in his negotiations with the State's Attorney Office, however, they do not guarantee that such an outcome will happen in your particular case. You absolutely need a defense attorney to handle this; he or she will know how to present them to the prosecution far better than you will. I do not mean this as a slight, but rather that an experienced defense attorney knows the local court system much more intimately than you can, and will have the knowledge to utilize these findings to their fullest.
The author is a Maryland attorney; however no answer given on Avvo is intended as legal advice or intended to create an attorney-client relationship.
The usual value of case law in criminal cases is to show the court or prosecutor how a court of appeals or supreme court has rule on some matter of law. Statutes are very skectchy, and the courts fill in details. What was offered and won or lost in prior cases is not so controlling, and as was stated, a defender in your county will know far more about how bargains are made or cases decided in your county. It may help you in shopping for an attorney. Always good to know more about the law, but an attorney will have studied for a long time.
We do not have a client/attorney relationship until you make an appointment, we discuss your case face to face, I accept a retainer, and we explictly agree to enter into representation.
I'm concerned with what you mean by "cases." The reason being is that I've heard many people tell me that they've heard about this case and that case, and it turns out they're citing to a newspaper article about a case. Don't bring a newspaper article about a case into court. Case law is written by judges and can be applied to make your argument stronger. However, lawyering and legal research is a skill usually best left to lawyers to do. You can try to prepare your case on your own, but your best bet is to hire an attorney. Bring your cases to the attorney and see what he or she thinks about them.
If you'd like to schedule a free initial consultation, call my office at 407-965-5519. I am licensed to practice in Florida only. My answer does not constitute legal advice or create an attorney-client relationship.