More than a dozen people have called for a new inquiry into the death of soul and funk legend James Brown, in a major CNN investigation that hears allegations that he and wife Adrienne Brown were murdered.

Brown died following a short illness on Christmas Day, 2006. The doctor who signed his death certificate tells CNN he has suspicions about the swiftness of Brown’s deterioration, especially after his condition had improved the previous day. “He changed too fast,” Marvin Crawford says. “He was a patient I would never have predicted would have coded ... But he died that night, and I did raise that question: What went wrong in that room?” Crawford says a nurse told him drug residue was found in a tube helping Brown to breathe, and says “somebody perhaps could have given him an illicit substance that led to his death”.

“There are legitimate questions about James Brown’s death that can only be answered by an autopsy and a criminal investigation,” writes CNN journalist Thomas Lake, who says 11 people told him that Brown’s death should be reinvestigated, adding to Brown’s late daughter LaRhonda Pettit and son-in-law Darren Lumar, who, before they died, also alleged Brown was killed.

They include Brown’s fourth wife Tomi Rae, Brown’s manager Frank Copsidas, and Daryl Brown, one of six heirs named in Brown’s will. And Reverend Al Sharpton, a friend of the singer, told Lake: “I’ve always had and still have a lot of questions … I wouldn’t mind a further investigation at all.”

Jacqueline Hollander, who amassed much of the evidence that points towards a possible murder, told Lake that her friend Adrienne Brown said she was forced to drop charges against her husband, of assault with intent to murder, after being intimidated by men working for Brown. Adrienne later made further allegations of domestic violence against Brown, but died before Brown could be tried.

Adrienne Brown’s official cause of death, in 1996, was an accidental overdose of painkillers following plastic surgery. But Lake hears from detective Steve Miller, who investigated Adrienne’s death, that a police informant, writing in a notebook seen by Lake, claimed Adrienne was murdered.

Hollander also told Lake that Brown had raped her, and threatened to have her killed if she told anyone about the assault. Seven people corroborated Hollander’s account that she was also covertly surveilled by Brown for years.