Sudden death can occur due to previously known or undiagnosed thyroid diseases. This case reports the death of a 21-year-old woman with symptoms suggestive of thyroid crisis. The victim’s family suspected foul play based on physical findings on the body. However, police investigation and autopsy results revealed a history of pre-existing thyroid disease. The autopsy findings showed enlargement of the thyroid gland and lung edema. Forensic histology also revealed chronic inflammation in the thyroid gland and bleeding in the lung tissue. In conclusion, the victim’s death was attributed to poorly controlled hyperthyroidism which leads to thyroid crisis. This case highlights the importance of proper management and treatment of thyroid diseases, as well as knowledge of physical signs related to postmortem changes. In this context, the case does not fulfill criminal elements but is more related to the pre-existing health condition of the victim. Therefore, a comprehensive analysis is conducted, considering the available information, including the victim’s medical history, witness testimonies, autopsy findings, and other relevant evidence. The investigation of this case holds broad significance, not only in the medical and forensic aspects but also in terms of legal and justice implications.