The headline on Stephanie Griffith's news story {Metro, Aug. 15} on accused killer Chander Matta's interview with a therapist at the Arlington County Jail, "Voices Drove Suspect to Violence, Report Says," inaccurately characterizes the facts reported in the story.

The story itself, while indicating that a "therapist" had found the accused to be experiencing "auditory hallucinations," indicates no finding by any therapist that the hallucinations caused or "drove" the alleged violent actions of the accused. This may be particularly important, since the story indicates that the accused may raise the insanity defense.

This seemingly small journalistic inaccuracy actually reveals a major misleading element typical in psychiatric testimony for the defense in insanity cases. Depending on the jurisdiction, the defense will generally try to show that either the defendant did not know what he was doing or that he couldn't control himself. The psychiatric evidence for these criteria comes primarily from the defendant's claims. Thus, the validity of expert testimony in an insanity defense is in large measure a function of the truth or falsity of the experiential claim of the defendant (e.g., "I heard voices") and the conclusion of the psychiatrist not only regarding the truth of the claim, but the assertion that if the claim is true, the hallucinations made it impossible for the defendant to appreciate the wrongfulness of his conduct or to conform his conduct to the requirements of the law.

The insanity plea is regarded by many as an abused, if not frequently used, plea. More precise insistence on the substance and validity of psychiatric conclusions would go a long way in minimizing the abuses that do occur. RICHARD E. VATZ Towson The writer is associate psychology editor for USA Today Magazine.