This case report describes an elderly patient with dementia resulting from B-12 deficiency and syphilis who was admitted to a forensic psychiatry hospital after killing his ex-wife with a gun. Despite current awareness of the occurrence of aggression and violence in patients with dementia, there had been no report discussing dementia secondary to an infectious or nutritional origin causing homicide or severe violent behavior. The article discusses possible mechanisms and several predisposing factors for violent behavior in the elderly, and complications related to use and access to weapons by demented patients and the elderly. The article recommends that, as the population ages, neuropsychiatric assessment by qualified professionals should be more available in the community. Detection of failing memory and other mental status changes in elderly patients is important because some types of dementia are reversible with appropriate treatment. Gun ownership among demented individuals should be reevaluated and access to guns should be limited. Clinicians evaluating the potential for violence of elderly individuals should inquire about the possession of weapons, including firearms. References