The role of the forensic pathologist is central to both identifying the cause and determining the manner of death. Distinguishing a suicide from a homicide or accidental event is essential to define whether third parties are involved in death. Suicides are most frequently performed using a single method; therefore, they can be defined as simple. The term "complex suicide" refers to a form of suicide in which two or more methods are applied by the victim, simultaneously or in chronological succession, to achieve the death. The different methods may have been planned in advance to prevent failure of the first method or may occur because the first method was not effective or was too painful, so the victim quickly seeks another way to complete the suicide. "Complicated suicides", on the other hand, are characterised by an unintentional secondary trauma following the suicidal act. This study analyses 35 complex suicides and 4 complicated suicides investigated at the Institute of Forensic Medicine in Brescia (Italy) during the period 1983-2022. Some data about the cases are discussed. This study aims to demonstrate how multiple lesions on the victim's body are not in themselves indicative of the intervention of third parties in their production, but complex and complicated suicides must always be considered.

Background: Congenital tracheal stenosis (CTS) caused by complete tracheal rings and absence of the pars membranacea is rare and potentially lethal in infancy. Agenesis or hypoplasia of the medullary arcuate nucleus (ARC), a chemosensitive component of the ventral medullary surface, has been implicated in disordered respiratory control in sudden perinatal and infant deaths. The coexistence of these two abnormalities is uncommon. Case: A 2-month-old male infant, apparently healthy, was found unresponsive on his parents’ bed in the early morning. The pregnancy was uncomplicated, aside from maternal obesity and tobacco use. Given a context compatible with either sudden natural death or accidental overlay/suffocation, a full forensic autopsy was ordered. An external examination showed diffuse cyanosis and minor superficial abrasions without significant trauma. An internal examination revealed heavy, congested lungs with petechiae and cerebral edema. The heart and great vessels were anatomically normal, and the ductus arteriosus was closed. Histological examination demonstrated congenital tracheal stenosis characterized by complete cartilaginous rings with absent pars membranacea and bilateral agenesis of the medullary arcuate nucleus. The overall findings supported an acute hypoxic–ischemic event during sleep. Conclusions: This case documents a rare, isolated CTS with complete rings and absent pars membranacea coexisting with bilateral ARC agenesis, providing a plausible organic substrate (“cum materia”) for sudden unexpected death in infancy (SUDI). It underscores the importance of standardized neuropathological examination with serial brainstem sections in SUDI investigations and of distinguishing explained SUDI from sudden infant death syndrome (SIDS), which remains unexplained after complete investigation (“sine materia”).