Forensic analysis of an unwitnessed fatal diving accident using in-water investigative reconstruction.

Unwitnessed diving fatalities present significant challenges for forensic investigation. We describe a fatal diving accident involving a 32-year-old experienced female diver during a deep night dive in freshwater. The diver became separated from her buddy and was recovered at depth in a head-down position, with evidence of entanglement of the central manifold valve of the twin-tank open-circuit breathing apparatus by a thin guideline. Autopsy findings were consistent with drowning. Technical examination of the diving equipment revealed no mechanical malfunction. Given the absence of eyewitnesses and inconclusive assessment of the accident circumstances, an underwater reconstruction was conducted in collaboration with a police diving unit. Using the original breathing apparatus and controlled underwater conditions, the reconstruction evaluated the technical feasibility of various accident scenarios, including entanglement, buoyancy redistribution, and loss of equipment control. The reconstruction demonstrated that unintentional formation of a simple guideline loop around the central manifold valve could occur during attempts at disentanglement. Partial inflation of the buoyancy control device and drysuit, combined with mechanical constraint of the breathing apparatus due to entanglement, resulted in inversion into a head-down position and displacement of the breathing apparatus following release of the waist strap. These configurations substantially impaired the diver's self-rescue capability and were consistent with objective findings documented at recovery. This case underscores the forensic value of controlled underwater reconstruction as a complementary investigative tool in unwitnessed technical diving fatalities and highlights its potential contribution to accident analysis and prevention.