Death by smothering and its investigation. This case report provides details from an extensive death investigation, the results of which led to the certification of suicidal manner of death by means of smothering in a pillow, without additional assistance from other persons or mechanical devices. This was the death of a chronically mentally ill person who was under currently approved professional treatment. Major investigative aspects of this case were the death-scene observations of the body, elimination of the possibility of homicide, and the study and analysis of the subject's psychiatric illness. Reasons for the uncommonness of reported deaths in this category are discussed. 