Federal agents would need the approval of the Justice Department as well as Peru to operate in Lima, and have the cooperation of local police, he said.
"I'm not convinced it is even the type of case the FBI would put the energy into," Garrett said.
Van der Sloot has behaved erratically since his arrest in Chile and his return to Peru. On Monday, he refused to speak to the judge in his case who traveled to the notorious Castro Castro prison to take a statement from van der Sloot.
After allegedly giving a detailed statement on how and why he killed Flores, he claims to have been tricked into signing it.
"During the interrogations I was very frightened and confused, and I wanted to leave," van der Sloot told the Dutch newspaper De Telegraaf in the notorious Castro Castro jail in Lima, Peru.
"'If you sign these papers you will be extradited to the Netherlands,' they were telling me all the time. In my blind panic I then signed everything, but I did not even know what was written down," he told the newspaper.
When asked by a reporter about the murder of Flores, van der Sloot replied, "I have been framed. What happened exactly, I will explain later."
He also complained to the newspaper that he has to share his prison cellblock with a Colombian murderer, a corrupt Peruvian general and rats that creep into his cell through the toilet at night.