The parents of an American software engineer found dead in his Singapore apartment last year have left the city-state before the end of a coroner's inquest. They say they have lost faith in the process and their lawyer says they will push for a U.S. congressional investigation.

Rick and Mary Todd believe their son Shane Truman Todd was murdered in June 2012 and that evidence of suicide presented by Singapore police was faked.

Rick Todd told reporters at the airport before they left for their Montana home that they felt there was no point in staying. His lawyer Gloria James-Civetta said the family's departure marks a "closed chapter" with regards to their involvement in the inquest, and confirmed their plans to initiate a congressional investigation into Shane's death.