The coroner's inquiry into American researcher Shane Todd's death was "comprehensive, fair and transparent," the United States Embassy in Singapore said on Monday.

Judge Chay Yuen Fatt had ruled earlier in the day that Dr Todd committed suicide by hanging.

In a statement, the embassy added that its officials attended the entire inquiry and were with the Todd family during their time in Singapore. The Todds quit the inquiry on May 21 and went home to the US two days later.

"The death of Dr. Shane Todd in June 2012 was a profound loss for his family, friends, and colleagues, and our heartfelt sympathy goes out to them," said an embassy spokesman.

Judge Chay delivering his finding on the case said the physical evidence pointed to the 31-year-old's death as a suicide as there was no foul play and no medical basis to find that it was a homicide.

"After considering all the evidence before me, I was also satisfied that there was no foul play involved in the deceased's death," he said in a 145-page decision.

The judge said there was no reason to doubt the authenticity of a suicide note found on Dr Todd's laptop at the scene of death, and there was also no evidence to suggest that the researcher had been involved with any sensitive research as part of his work at the Singapore Institute of Microelectronics (IME).

"The deceased was not in possession of confidential and valuable classified information in the course of his employment at the IME," he added.