Tattoo visualization using cross-polarized lighting and infrared photography

Identification of the deceased is a critical responsibility of the death investigation system. If visual identification is inconclusive, tattoos can provide secondary identification but may be difficult to visualize at various stages of decomposition. We describe the case of a 35-year-old male found submerged underwater by police after swimming at a pier. The decedent was last seen earlier that day. Signs of immersion including sodden hands, feet, and clothing, wet sand on the torso and legs, and heavy edematous legs were observed. The post-mortem blood alcohol concentration was 427 mg/100 mL; signs of recent traumatic injury were not present. The immediate cause of death was drowning as a consequence of ethanol intoxication. When pulled from the water, the decedent's shoulder tattoo was not visible. Cross-polarized lighting and infrared photography visualized the tattoo to help confirm identity. These photographic methods were compared to hydrogen peroxide and optical coherence tomography techniques and described in detail to assist with future cases.