Dressed in lock-up attire of a red polo shirt and blue shorts, with his hands and legs secured, he kept his head down and followed DSP Tan down to the canal.

It was only after returning to the scene and being made to recount in detail what happened that Yap broke down.

In lock-up, he sobbed and told officers that he was depressed and very down, said DSP Tan.

"He was unable to continue on," said DSP Tan. "He was crying constantly, so we had to make an assessment and sent him to Changi Medical Complex. He was warded there straight away."

Yap was later remanded at the Institute of Mental Health for psychiatric assessment, labelled a suicide risk and monitored.

His time in psychiatric assessment came back with the diagnosis of major depressive disorder of moderate severity around the time of the offences.

After this finding, the prosecution lowered the charges of murder against Yap - the second charge for Aston's death was given to him in February 2022 - to culpable homicide not amounting to murder. The charge amendment meant that Yap no longer faced the death penalty but a maximum of life imprisonment.

He entered a guilty plea in August 2023, and his lawyers Mr Choo Si Sen, Mr Patrick Nai and Ms Choo Yean Lin submitted to the court a letter Yap had written.

In the letter, he apologised for the mayhem and trouble he had caused. He said he was "overwhelmed by sadness and hopelessness" and had "totally lost faith that my two sons would be taken care of in the future".

He had hoped that taking his two sons with him "would end their unfair suffering" and wished for "a quick death and to be quickly served with a death sentence".

He said this was "the most lenient punishment" to him, and would allow him to join his two sons.

When this was read out in court, Yap, who was standing in the dock, was seen with tear-filled eyes.

Despite the defence's call for the two jail terms for the boys' deaths to run concurrently, the judge ruled that the sentences must run consecutively to "accurately reflect the overall criminality of (Yap's) conduct which led to the loss of two innocent lives".

Yap was given 14 years' jail - seven each for Ethan and Aston.

"In my view, the overall sentence which I have imposed seeks to balance the fact that a heinous and serious set of offences occurred on Jan 21, 2022 and the fact that the accused suffered from (major depressive disorder) at the time of the offences," said Justice Vincent Hoong.

"The sentences cannot in any way compensate for the tragic loss of two innocent young lives. One hopes, however, that the accused will use this time to reflect on the irreversible harm he has caused to his family as a result of his misconceived belief that he would be easing the suffering and pain of the victims and of those around him by committing the offences."

The Dad Who Killed His Twin Sons

Investigating the crime that shook Singapore