On March 10, 2013, Professor Winston Koh, 50, embarked on his fourth open-water dive with three other trainees at Rayner's Rock, a dive site off Pulau Dayang in Malaysia.

It was part of a National Association of Underwater Instructors Scuba Diver Course organised by Mako Sub-Aquatics, a diving school based in Singapore.

The trainees went into the water one by one from the dive boat before making their descent underwater.

Prof Koh and two other trainees dived into the water first. The last trainee was accompanied by a dive instructor.

No trail line - used to keep divers together - was used.

Upon reaching a depth of seven metres, the instructor saw the three trainees but Prof Koh was not in sight.

Meanwhile, the currents became stronger and soon, the dive was aborted.

The trainees ascended to the water surface, while the instructor tried to search for Prof Koh.

One of the trainees was swept away by the strong water currents, but was eventually picked up by another dive boat in the vicinity.

Despite a surface search, Prof Koh was still missing.

During an underwater search, the instructor found a weight belt, scuba-diving tank and buoyancy compensator used by Prof Koh.

The next day, Mrs Caroline Koh arrived at Pulau Dayang with her daughter, her brother-in-law and his wife.

Four days later, on March 14, 2013, Prof Koh's body was found by the Malaysian Marine Police on the shores of Pulau Dayang.

He had drowned.