Wyo. Stat. § 7-11-305

(a) When a defendant couples a plea of not guilty with a plea of not guilty by reason of mental illness or deficiency, proof shall be submitted before the same jury in a continuous trial on whether the defendant in fact committed the acts charged, on the remaining elements of the alleged criminal offense and on the issue of mental responsibility of the defendant. In addition to other forms of verdict submitted to the jury, the court shall submit a verdict by which the jury may find the defendant not guilty by reason of mental illness or deficiency excluding responsibility.

(b) The prosecution shall prove beyond a reasonable doubt all the elements of the offense charged. Every defendant is presumed to be mentally responsible. The defendant shall have the burden of going forward and proving by the greater weight of evidence that, as a result of mental illness or deficiency, he lacked capacity either to appreciate the wrongfulness of his conduct or to conform his conduct to the requirements of the law.

(c) Only the designated examiners who examined the defendant pursuant to W.S. 7-11-303 or 7-11-304 are competent witnesses to testify as to the defendant's mental responsibility.

(d) In addition, the state and the defendant may summon other expert witnesses who did not examine the defendant. Such experts are not competent to testify as to the mental responsibility of the defendant; however, they may testify as to the validity of the procedures followed and the general scientific propositions stated by other witnesses.

(e) The designated examiner who examined the defendant may testify as to and explain the nature of his examinations, his diagnosis of mental illness or deficiency of the defendant, and his opinion as to the defendant's ability to appreciate the wrongfulness of his conduct or to conform his conduct to the requirements of law. The designated examiner may be cross-examined as to his competence and the credibility of his diagnosis and his opinion.