Scott Hodes, who used to be the top lawyer in the FBI records office, said agency policy requires records on prominent people to be preserved, USA Today reported.
"You are not supposed to destroy records that are historically valuable," Hodes said. "Somebody should have known who Walter Cronkite was."
USA Today had requested Cronkite's files under the Freedom of Information Act but was told some of the documents had been destroyed in 2007.
The FBI had no immediate comment other than to say they work with the National Archives to preserve historically significant documents.
Cronkite was the anchor of the CBS nightly news from 1962 to 1981. He died in July at the age of 92.
Astronomers offer more expansive view of universe
McPhee, Cokas 'working on their marriage' after affair