A US scientist found hanged in Singapore last year had been suffering a relapse after a previous bout of depression, his local psychiatrist said Thursday, as his parents insisted he was murdered.
High-tech researcher Shane Todd "had a lot of worrying thoughts that he could not control", Singaporean psychiatrist Nelson Lee said on the fourth day of a coroner's inquiry to determine the cause of his death.
"Following my consultation with Shane, I diagnosed him to be suffering from a relapse of his depression and noted that he had a significant component of anxiety," he said in a prepared statement read at the inquest.
Todd was referred to Lee three months before he died on June 24, 2012 after he complained to his doctor of insomnia and an inability to cope with work-related stress.
Lee said he prescribed anti-depressant pills after Todd was assessed to have been suffering from a relapse of a previous bout of "major depressive disorder".
Todd's parents, who are attending the inquest, insisted Thursday that their son, aged 31 when he died, was murdered and said they would give details about who they think killed him when they testify at the inquest.
"We have our suspicions on who that (killer) may be, but we are not going to get that out until we get it out in court," Todd's father Rick, an airline pilot, told reporters.
The state counsel at the inquiry issued a statement late Wednesday asking the parents to provide evidence for their claim that he was murdered, rather than committing suicide as medical experts said.
The inquest is due to last until May 28. A verdict is expected by late June.
The parents allege he was killed because of his work for a Singapore institute with purported links to a Chinese telecom firm accused of involvement in espionage.
Also testifying on Thursday was forensic pathologist Wee Keng Poh, who supervised the autopsy of the late scientist. He told the inquiry the cause of death was "asphyxia due to hanging".
Wee said "ligature strangulation" was unlikely as there were no injuries found other than those around the neck.
Wee also disputed findings by Edward H. Adelstein, a US pathologist engaged by the Todd family who had concluded that the researcher was killed by "garroting" and that there was evidence he had put up a fight.
Findings by Adelstein of "multiple blunt traumas" on Todd's hands -- which the US doctor said indicated he engaged in a fight -- were "post-mortem lividities" that formed after the autopsy, Wee said.
Two US-based doctors, acting as independent experts, had reviewed the autopsy report and said the findings were consistent with suicide.
Singapore police who inspected the apartment where the researcher was found hanged on June 24, 2012 have told the inquiry they saw no signs of a struggle.
The state counsel in his opening statement Monday said Adelstein appeared to have based his opinion on the autopsy report and some pictures.
Todd's former employer, Singapore's state-linked Institute of Microelectronics, and Chinese telecoms giant Huawei Technologies, have denied the family's claims that they worked together on a project involving Todd.
At the time of his death Todd had just finished a stint with the institute, where he was part of a team working on gallium nitride, a tough semiconductor material that can be used in radar and satellite communications.
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.