Jeffery Yao, Massachusetts man who killed Deane Stryker while she was studying at Winchester Public Library, found not guilty due to mental illness Updated 8:05 AM; A Massachusetts man charged with fatally stabbing a woman studying to become a doctor at a public library — and injuring a man who came to her aid — was found not guilty Wednesday because of his mental illness. Jeffery Yao, 27, of Winchester, was sent to a state mental health facility by Middlesex Superior Court Judge Kathe Tuttman after a one-day, jury-waived trial. Yao was evaluated by three experts — two for the defense — who each found that he lacked criminal responsibility because “he did not have either substantial capacity to appreciate the wrongfulness of his conduct or the ability to conform his conduct to the requirements of law,” according to a statement from the office of Middlesex District Attorney Marian Ryan.