Concluding a week of dramatic testimony at the country’s Truth, Reconciliation and Reparations Commission (TRRC), Amadou Badjie said that Mr Jammeh wanted the two men, Alhaji Ceesay and Ebrima Jobe, killed and “chopped into pieces”, AFP adds.
Under questioning, Mr Badjie, who was part of a group known as the Junglers, said it was a hit squad for the former president.
Mr Jammeh wanted the two Gambian-Americans killed as he suspected they were plotting a coup.
"These two people were suffocated to death and their heads chop off. We buried these corpses in one grave," Mr Badjie said, AFP reports.
Earlier this week, the TRRC heard testimony that the former president ordered the killing of a well-known journalist and a group of migrants.
Mr Jammeh - who now lives in exile in Equatorial Guinea - always denied any involvement in the deaths of the migrants or the journalist.