Rule 15. Expert witnesses and interpreters.

(a) The court may appoint any expert witness agreed upon by the parties or of its own selection. An expert so appointed shall be informed of his duties by the court in writing, a copy of which shall be filed. An expert so appointed shall advise the court and the parties of his findings and may thereafter be called to testify by the court or by any party. He shall be subject to cross-examination by each party. The court shall determine the reasonable compensation of the expert and direct payment thereof. The parties may call expert witnesses of their own at their own expense. Upon showing that a defendant is financially unable to pay the fees of an expert whose services are necessary for adequate defense, the witness fee shall be paid as if he were called on behalf of the prosecution.

(b) The court may appoint an interpreter of its own selection and shall determine reasonable compensation and direct payment thereof. The court may allow counsel to question the interpreter before he is sworn to discharge the duties of an interpreter.