Duncan died last year, weeks after suffering a heart attack at his home. Manigault was credited with reviving him by performing CPR and getting him to the hospital.
Jackson brought the painful subject up during a confrontation with Manigault, who was her teammate on Sunday's episode of "Apprentice."
"Omarosa is the most evil person I have ever met. She's a no-good, conniving, scheming, cut-throat, probably pulled the cord on Michael Duncan Clarke," E! News quoted Jackson as saying.
Jackson also said Manigault probably caused Duncan's heart attack.
Show host and executive producer Donald Trump later fired Jackson after her team failed to create a successful 5-minute soap opera for Crystal Light, E! said.