Just before dawn at around 6 A-M on Tuesday a civilian diver went into the rough waters around the Sewol-ho ferry to search for victims.
He was trying to install new guideline ropes to the fifth floor of the ship to help in the search for the dozens of bodies that remain unaccounted for.
After about five minutes, at a depth of about 25 meters, the 53-year-old diver lost communication with fellow divers on the surface of the water, prompting his colleagues to go and rescue him.
Only known by his surname Lee, the veteran diver was found unconscious, without his diving equipment on and with his communication and air supply cords tangled.
"As he was found unconscious, officials used an automated external defibrillator, and conducted CPR on him right away."
The diver was transported by helicopter to the nearest hospital in Mokpo, but died soon after arriving.
This is the first fatality among divers in the nearly three weeks of search and rescue operations.
Officials are still trying to determine his exact cause of death.
"An X-ray of his chest showed no irregularities, but a scan showed that his skull was filled with air."
After a brief delay, search and recovery operations were conducted throughout the day on Tuesday.
Officials say divers have now searched all the main compartments of the ship at least once, but will revisit them again to look for more victims.
Authorities also continue to investigate what caused the sinking of the ship-- although improper stowage, and overloading of cargo three times the safety limit, are seen as the probable causes.
So far 19 people have been arrested in the investigation including crew members and an executive of the ferry's operator, the Chonghaejin Marine Company.
The executive was arrested on charges of malpractice related to the company's finances.
Connie Lee, Arirang News.