"Now that he's been buried and embalmed, you don't have the ideal situation," said Dr. Daniel J. Spitz, a forensic pathologist and toxicologist and the chief medical examiner for Michigan's Macomb and St. Clair counties.

Spitz co-wrote the book "Medicolegal Investigations of Death," considered the bible of forensic pathology that pathologists worldwide use.

"If this were me, I'd be hoping with an autopsy every other cause of death is rejected," Spitz said. "You don't want to have a competing cause of death when you present your case in court."

In this next step in the investigation, scientists will examine Khan's brain, the liver and even solid organs to try to detect the presence of cyanide so they have more than one test showing it's what killed him -- and a better sense of how it was introduced into his body.

"Many people think, with this kind of poisoning being rare and something that may not be seen, that this would be a murder someone could get away with," Geller said. "But clearly it is not, since they did figure out this was cyanide, and there is a very good likelihood someone will get caught."