A Singapore state coroner ruled that a US scientist found hanged in the city-state in 2012 committed suicide and was not murdered as his family claims.

State coroner Chay Yuen Fatt said at a public hearing that Shane Todd died from "asphyxia due to hanging", adding that "I was satisfied that there was no foul play".

Chay also said that evidence presented at an open two-week inquiry in May proved "beyond a reasonable doubt that the deceased had committed suicide".

The body of the 31-year-old electronics researcher was discovered by his girlfriend in his flat in June 2012, sparking a controversy that reached the highest levels of the Singapore and US governments after his parents refused to accept suicide findings by the Singapore police.

Todd's parents say he was murdered as part of a conspiracy involving a Chinese technology firm.

Monday's verdict by the Singapore coroner cannot be appealed.

Earlier, the Singapore government rejected the murder theory and said Todd killed himself after a bout of depression.

Government lawyers cited suicide notes left by Todd on his laptop computer, a psychiatrist's testimony that he suffered from depression, and a browsing history showing he accessed suicide websites before his death.

But the Todd family remains insistent that he was murdered because of his work at his former employer, Singapore's state-linked Institute of Microelectronics (IME).

They claim that he was involved in a secret project for Huawei Technologies, a Chinese telecom giant seen by Washington as a security threat.

IME and Huawei said they only held preliminary talks on a potential project with commercial applications, but did not proceed.