There was overwhelming evidence that American researcher Shane Todd killed himself, the State said in its closing submissions on Monday morning.

In contrast, there was a "conspicuous absence of any evidence" that supported the theory that the ex-Singapore Institute of Microelectronics (IME) employee was murdered, despite his parents' allegations, said Senior State Counsel Tai Wei Shyong.

"During the course of the inquiry, counsel for the next-of-kin questioned the professionalism of the police and called into question the findings of independent Health Sciences Authority experts," Mr Tai read from prepared remarks. "However, they did not provide any evidence of how Shane might have been killed, or by whom," he said in his closing submission for the coroner's inquiry into Dr Todd's death.

The State Coroner will deliver his verdict on July 8.

Mr Tai pointed out that the family's medical expert, Dr Edward Adelstein, had changed his initial opinion that Dr Todd, who was 31-years-old, was murdered by garroting to possibly having been killed by a stun gun or an arm-lock. However, he offered no evidence to support his claims, and the allegation was dismissed by medical experts engaged by the state.

Mr Tai also said that the hard disk the Todds claimed they had retrieved from Dr Todd's Chinatown apartment after he was found hanging - a crucial piece of evidence they were relying on to allege foul play - was in fact handed to them by the police after it was examined by the investigations officer.

There were also no outgoing calls from Dr Todd's phone after it was seized by police. Outgoing GPRS transactions could have been the result of background apps with no human intervention, he added. "It is clear from the medical forensic evidence that the medical cause of Shane's death was asphyxia due to hanging," said Mr Tai.

Lawyers for the IME added in their closing submission that the evidence showed Dr Todd could not have been murdered because of "valuable" trade secrets. The lawyers' 252-page submission spanned Dr Todd's employment record at the institute, copies of all related emails between him and his superiors and even pages from his PhD dissertation.