In determining a person's competence to stand trial, there are host of factors that may be evaluated. First, it's the Commonwealth's burden to offer expert testimony to the effect that an individual is competent beyond a reasonable doubt. The Commonwealth must show that the evidence is sufficient from their expert to prove that a person had the capacity to stand trial. A non-expert may express a general opinion as to the mental capacity of an individual, as expressed in Commonwealth v. Knight of 1976. This specifically goes to an individual who knows the defendant and has personal experience with them.
Evidence of state of mind is equally important in determining the competence to stand trial. If a defendant or their Lehigh County criminal lawyer believes that they are not capable of standing trial, they must come with significant evidence. In Commonwealth v. England from 1977, the court determined that it has been the law for a long period of time in the Commonwealth that an accused person statements to third persons maybe offer to indicate the mental state of the accused where his sanity is an issue. In this context the accused made comments and they may be evaluated in the same manner as his nonverbal behavior and can be determined to being reflective of the condition of his mind. The court stated that you can recognize that one's verbal conduct may be just as illuminating upon the state of mind of the declarant as his nonverbal conduct, and that text writers have recognized the wisdom of excluding irrational expressions which are offered to show mental incompetence, regardless of their form, from the constraints of the hearsay rule.
The court in Commonwealth v. Young from 1980 stated that it seems clear that the law in Pennsylvania is that evidence of lay witnesses alone can be sufficient to establish the sanity of a defendant who has offered expert testimony as to his insanity. The Commonwealth me meet its burden by testimony concerning the defendants actions, conversations, and statements at the time of the crimes from which the jury can infer that he knew what he was doing when he committed the crimes and that he knew that his actions were wrong.