HELENA, Mont. (AP) - The parents of a software engineer whose body was found last June hanging in his Singapore apartment are calling for the U.S. to take over the investigation.

Rick and Mary Todd of Marion, Mont., say they have found evidence that leads them to believe their son may have been killed over his semiconductor research in New Jersey.

Singapore police originally told them they believed Shane Todd had killed himself. The investigation is ongoing.

Rick and Mary Todd say their son told them months before his death that he believed his employer was asking him to do something that might hurt U.S. national security.

They've enlisted the help of two U.S. senators to bring their case to the Obama administration's attention and plan to meet with Singapore's U.S. ambassador.