American engineer Shane Todd had searched for suicide-related websites 19 times in the four months leading up to his death, said Senior State Counsel Tai Wei Shyong in his opening statement during the first day of the Coroner's Inquiry into his death on Monday.

After the 31-year-old was found hanged in his apartment near Chinatown on 24 June last year, 19 pills containing Citalopram, an anti-depressant, were also found in his home, a conserved shophouse, said Mr Tai.

Dr Todd was found dead shortly after he quit the Singapore Institute of Microelectronics, which he had joined in 2010. It was his first job after graduating with a doctorate from the University of California, Santa Barbara.

Four witness who took the stand on Monday morning, including his girlfriend Shirley Sarmiento, neighbour Michael Goodwin, and friends Ali Miserez and Bart Richard Lendrum, said that he had been stressed over his work, especially after he had transferred to a new research group in March 2011.

He had confided in his girlfriend that he was unhappy partly because his colleagues were mostly Chinese who spoke to each other in Mandarin, which he did not understand.

Ms Sarmiento added that Dr Todd had said he was working in a "dishonest environment" and that his boss had "stolen his team's idea". Mr Lendrum said Dr Todd had complained that his co-workers were not as hardworking as him and did not meet his standards, while Mr Goodwin said Dr Todd had once confessed to dropping a $10,000 piece of equipment in front of his colleagues and was embarrassed by it.

Ms Sarmiento added that Dr Todd had told her on one occasion that there were "heavy hands" coming after him, and that he was doing work which could get him into trouble with the United States government.

The inquiry will resume after lunch, with police officers expected to take the stand.