Three pathologists involved in the coroner's inquiry into the death of American engineer Shane Todd in Singapore said the evidence in the case points to death by hanging and not strangulation.

Senior consultant forensic pathologist Wee Keng Poh of the Health Sciences Authority, who supervised the post-mortem examination, also said that he disagreed with the finding of a pathologist engaged by Todd's parents that he had been involved in a fight for his life and was killed by strangulation with a cord or wire.

Todd, 31, was found hanging from a black strap in front of a closed toilet door in his bedroom in his apartment on the second floor of a conserved three-storey shophouse on June 24, 2012.

Letters to his family members and girlfriend were found on his computer with a passwords left on a post-it.

The apparent suicide came three days after Todd quit his job with the Institute of Microelectronics, a unit of Singapore's state-run Agency for Science, Technology and Research. He was expected to return to the United States on July 1 last year.

Singapore police has classified the case as suicide, while Todd 's parents suspected foul play and sought help from US lawmakers to put pressure on Singapore.

Edward Adelstein, deputy medical examiner in Boone County and Callaway County, the United States, engaged by Todd's parents, said in a report last year he was of the opinion that Todd was " killed by an encircling ligature (garroting) and death occurred quickly," and that after his death he "was suspended by a broader based ligature in an attempt to obscure the original thinner ligature."

Adelstein also raised questions about some of the marks on Todd 's hands.

However, Wee told the court on Thursday that such marks were likely due to a process known as post-mortem lividity, which is the pooling of blood that oozes out of blood vessels after death and causes discoloration.

David Fowler, chief medical examiner for the State of Maryland, and Valerie Josephine Rao, chief medical examiner of District 4 and part of District 3, Jacksonville, Florida, both said in their reports that they agreed with Wee.

Fowler said the redness on the back of Todd's neck was likely abrasion caused by the towel found wrapped around his neck. The pattern of the redness matched the weave of the towel.

They said all of the marks on Todd's body were consistent with death by hanging. The mark on his neck was an inverted "V" which is typical of hanging. If Todd had been garroted, the mark would have been a horizontal circle encircling whole neck. Instead, there was a gap of 4 cm that led up to the noose.

There was no sign of bleeding from broken blood vessels in his eyes, nor was there any bleeding in the internal structures of the neck, both of which would indicate strangulation, they said.

Todd's parents had also raised questions about a hard disk drive, but Singapore officers said they had accessed it after Todd 's death, and experts in the United States have said they found the evidence consistent.

The high-profile coroner's inquiry opened on May 13, with some 60 witnesses lined up. Half of the witnesses, including Todd's girlfriend, his neighbor next door and the officers, are expected to take stand.

Senior State Counsel Tai Wei Shyong said in the opening statement on Monday morning that the internet history on Todd's laptop showed that depression and suicide-related websites had been accessed from his laptop in the months before his death.

His girlfriend Shirley Sarmiento, a Philippino who is working as a nurse at a local hospital, was the first to find Todd hanged in his apartment. His neighbor Michael Goodwin, alerted by the woman screaming, asked their neighbors to call the police.

The officers upon arriving at the scene observed "no signs of forced entry" and "no signs of injury on the body."

Sarmiento told the court that Todd told her that he was stressed over his work and that "he had been depressed since October 2011." His neighbor and friends also said he was stressed over work.

Todd had also seen a psychiatrist and had been prescribed anti- depressant pills, according to Tai.

Todd's mother indicated earlier after the coroner's inquiry began that she still believed her son had been murdered.

Todd's parents had insisted that they suspected foul play over Todd's work at the Institute of Microelectronics, "possibly" over what they said could be a technology transfer involving Chinese telecommunications equipment maker Huawei.

Huawei has denied the allegation, saying that the collaboration mentioned by Todd's parents did not even proceed.

The case has been gradually high-profile as media in Britain and the United States splashed headlines over the incident.

Singapore police recently refuted a Financial Times report on the death of American engineer Shane Todd as "inaccurate" and " mischievous." Authorities in Singapore have said that they adopt standards that were among the highest in the world.

The case also led to apparent diplomatic pressure on Singapore after Todd's family had sought the help of US lawmakers, who subsequently tried to block US funding to IME.

While admitting that he did not have the facts, US senator Max Baucus said he had "deep concerns about potential foul play and potential breaches of national security."

Some of the US lawmakers have also been pushing for American investigators to take the lead in reviewing the case.

Kishore Mahbubani, a former diplomat of Singapore, said he was appalled at Baucus jumping the gun and trying to pressure by forcing Singapore to give the Federal Bureau of Investigation (FBI) oversight of the case before the coroner's court had completed its inquiry.

"This goes against all international laws and norms. The United States would never allow a foreign police force to oversee an FBI investigation. Nor would it allow any foreign intervention into its judicial inquiry process," he said.