The fax was from a Canadian pharmacy, offering imported IV chemo drugs at suspiciously deep discounts.
"It was inconceivable anybody would do this. It made no sense. Why you would start ordering these drugs from a pharmacy you have no idea or clue about," Rao said.
After all, delicate cancer medicine requires meticulous processing. Illegally imported drugs could be fake - or even toxic.
But soon after Rao got that fax, a fellow oncologist confessed that he was buying those cheap chemo-drugs.
"That's when I started to have sleepless nights," Rao said.
"When you can't be sure of the origin of the drugs, what kind of risk does that put the patients at?" Attkisson asked.
"Buying it from non-FDA sources, you are putting patients' ... lives at serious risk," Rao said.
What is their motivation?
Rao said: "Their biggest motivation is profit."
That's because they aren't passing the savings on to patients. Doctors are making an extra buck for themselves.
Just look how much: in the United States, a single treatment of this ovarian cancer medicine costs more than $4,000. The imported version: about $3,000. A doctor can walk off with more than $1,000 extra profit. It can add up to millions a year per doctor.
And often, it is taxpayers taking it on the chin.
"Then the doctors are charging full price to Medicare or Medicaid and pocketing the difference," Attkisson asks.
"Exactly," Rao said.
That's how Dr. Rao got the feds involved: Ripping off Medicare ripping off taxpayers.
He played detective and uncovered enough evidence for the FBI to raid a Texas office of the Canada pharmacy. There, they found names of a hundred doctors from across the country who were customers.
There are still lots of loose ends - U.S. officials won't say whether they're pursuing other doctors, or if the Canadian pharmacy violated any laws. It's still up and running.
And there's no way to know if patients have been hurt, since their complications would likely be blamed on cancer.
So that's a way the physician can get away with it.
Get away with lining their pockets ... while patients put their trust, and lives, in their doctors' hands.