give letter to police officer named in disclodure (per prosecutor instruction "to investigate letter"),
The reason something needs to be certified is people will print out all kinds of letters on their home computer and bring it in. (I have seen this happen).
Being it is a 5k fine you want to make sure you have what the courts will accept. If not you could walk out with a 5k fine. It is pretty simple. I testify that I stopped and believed that the driver who was the owner was not insured and could not produce proof. That is all that is needed for a conviction. The driver then has to provide the proof of insurance and it has to be in a form that they courts will accept.
Like others have said find out from the prosecutor what they require and bring it. I will never take proof as once I lay the charge it is the prosecutors responsibility to deal with it not mine.