But one of them never completed the run and was found lying unconscious in the camp in Old Choa Chu Kang Road.

Mr Roslan Saharo, 18, who was just two months into his basic training, would never wake up again.

After two days in a coma, his family decided yesterday morning to take him off life support.

Relatives said doctors told them he had heat stroke which caused multiple-organ failure and left him brain dead. An autopsy will be performed today to determine the cause of death.

Family members and relatives were devastated by his sudden death. 'He was such a lively and jovial boy. We will miss his laughter and never-ending smile,' said uncle Dzulkifli Wasnam, 33.

They are now trying to find out the circumstances of his death.

Two of his uncles said a police officer told them at the hospital that Mr Roslan was discovered missing from the group only after the run ended.

But last night, a police spokesman told The Straits Times an instructor had seen him 'stumble and fall' and he was given 'prompt medical attention'.

His brother, Mr Riduwan Saharo, who was a combat medic during his national service days, said there should have been a 'last man' at the back of the group to ensure no one lagged behind.

'Where was the last man when my brother fell?' asked the 26-year-old. 'And where was his buddy?'

Mr Roslan's family said he was healthy and active - he played floorball for Institute of Technical Education College Central.

But on Sunday, when he had to report back to camp, he was coughing badly and told his father he was ill, said his sister Rubiah Saharo, 29. She advised him to see a doctor, but he said he was rushing back to camp.

One of Mr Roslan's uncles said the police told them an instructor had asked the group before the run if anyone was not feeling well, but Mr Roslan did not speak up.

Police said they will render support and assistance to Mr Roslan's family.