Wichit Police were notified of the incident at 12:08pm, when the 191 emergency centre reported that a man had been found unconscious on the southbound lanes at the entrance to the Darasamut Underpass.
Patrol officers were dispatched to the scene, where they found the man, later identified as 45-year-old Turkish national Nadiroglu Zaur, lying unconscious.
Rescue workers and medical personnel performed CPR at the scene before transporting him to Bangkok Hospital Siriroj, where he was later pronounced dead.
Police confirmed that the man had jumped from an overpass above the tunnel entrance. No other people were reported injured and no property damage was recorded.
Wichit Police reported that the incident is under investigation. Mr Zaur had left behind his black backpack and phone on the pedestrian bridge above.
The case is being handled under the supervision of Wichit Police Station chief Pol Col Somsak Thongkliang, with Pol Lt Col Kraison Pakaree leading the investigation.
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