Lawyers for the Singapore government told a coroner's inquest on Monday that an American scientist found hanged in the city-state last year killed himself and was not murdered as his family claims.

Summing up state agencies' findings on the death of electronics engineer Shane Todd in June 2012, they said "it is clear from the medical forensic evidence that the medical cause of Shane's death was asphyxia due to hanging."

The coroner's verdict, which cannot be appealed, is scheduled to be handed down on July 8. Public hearings on the case were held from May 13-27.

Todd's family stormed out of the hearings on May 21, saying they had "lost faith" in the proceedings and describing it as one-sided. They later said they may have the body exhumed in California for further tests.

The Singapore 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.

"The conspicuous absence of any evidence to support the next-of-kin's homicide theory must be viewed in juxtaposition with the overwhelming evidence pointing inexorably towards suicide," said a summary read in court by senior state counsel Tai Wei Shyong.

He concluded by saying that the "homicide case theory is entirely misplaced and unfounded, and that Shane's death was a suicide."

In statements to the inquest, Todd's parents said he feared he was being made to compromise US national security in a secret project involving a Chinese telecom firm accused of international espionage and a state-linked Singapore institute that employed their son.

The two firms they implicated -- the Institute of Microelectronics and China's Huawei Technologies -- said they only held preliminary talks on a potential project with commercial applications, but did not proceed.

A US congressional committee last year labelled Huawei and ZTE, another Chinese telecom firm, as potential security threats that should be excluded from US government contracts and barred from acquiring US firms.

During the hearings, the Todd family's star witness, US pathologist Edward Adelstein, recanted an earlier theory that Todd was garroted with a cord in his own apartment.

He presented a new theory: Todd was killed by assassins who used a stun gun before choking his neck and then hanging him to make it look like a suicide.

But Adelstein presented no evidence and two other US pathologists testified in support of Singapore police findings that Todd hanged himself from his bathroom door.

Witnesses also testified that Todd showed signs of heavy stress in the days before his body was discovered by his girlfriend.