Multiple sources with direct knowledge tell TMZ ... Graceland officials, along with people from Riley Keough's camp, were in touch with the FBI Tuesday, and we're told the agency is "interested" in conducting a criminal probe.

We're also told the would-be victims are in the process of contacting the Tennessee Bureau of Investigation.

As we reported, a judge was supposed to rule as to whether the foreclosure auction could move forward, triggered by an alleged unpaid $3.8 million debt Lisa Marie Presley never paid, supposedly using Graceland as collateral. Well, everything we've seen connected to this foreclosure looks sketchy, and that's a generous take on what really went down.

We're told Lisa Marie never took out a $3.8 million loan, and the notary who supposedly witnessed Lisa Marie signing the loan documents says that never happened ... she never even encountered Lisa Marie, ever.

The entity behind the foreclosure backed off the auction Wednesday, after a judge temporarily halted it. That's especially weird ... walking away from a supposedly unpaid $3.8M loan.

Our sources say ... the folks connected to Graceland believe one individual is behind the fraud, and they know that person's identity.