My orthopedic surgeon say he will not do back surgery until I come crawling into his office. After failing steroids and opiates.
Either way, killer was a nut, or marginally sane person driven crazy by perception or reality of unrelieved pain.
People react differently to medications. If Vicodan can cause anger issues then we may see the extreme anger issue in one or more patients, while most will be rational though perhaps irritable.