Gen. Norton Schwartz, the Air Force chief of staff, told reporters that the actions taken by the mortuary at Dover Air Force Base in Delaware were based on written guidance issued in March 2002 by David Chu, who was the Pentagon personnel chief under Defense Secretary Donald Rumsfeld.
Defense Secretary Leon Panetta directed that the families be briefed on past practices of remains disposal.
Pentagon Press Secretary George Little said Wednesday the briefings would be offered "within the next few weeks."
"We intend to make the facts about that past policy known to the loved ones of those who died," Little said, noting that in 2008 the practice of disposing of remains in landfills was ended.
Chu did not specifically mention dumping incinerated residue of 9/11 remains in a landfill, but his words might have been interpreted to allow that final step.
The Pentagon released a copy of the Chu memo, which was addressed to Thomas White, the Army's top civilian official at the time. The Army oversaw the Air Force's mortuary activities at Dover and elsewhere.
Schwartz said he only became aware on Tuesday that some portions of remains were dumped in a landfill.
"To the best of our knowledge at this moment in time, we followed those disposition instructions" from Chu, Schwartz said. He added that "there is a requirement for us to validate that that is the case."
The Chu guidance did not mention disposing of any remains in a landfill. It said unidentifiable remains that were mixed with fragments of "non-biological material" from the attack site were to be "treated in the same manner as any biological tissue removed for surgical or diagnostic purposes (i.e. disposition by incineration)."
That appears to leave open the question of whether disposal in a landfill was permitted.
The disposal issue came to light Tuesday when the head of an independent panel, retired Gen. John Abizaid, released a report that assessed management problems at the Dover mortuary. His work was triggered by revelations last fall about the mishandling of remains of American war dead at Dover in 2010.
The Abizaid report mentioned in passing that the practice of dumping of some portions of remains in a landfill began shortly after the Sept. 11, 2001 terrorist attacks. The report said several portions of unidentifiable remains from the Pentagon attack and the site of the hijacked plane that crashed near Shanksville, Pa., were cremated, incinerated and dumped in a landfill.
Asked about the Abizaid report on Tuesday shortly after its public release, Schwartz and Air Force Secretary Michael Donley said it was the first time they had heard of 9/11 remains being disposed of in a landfill.
At a previously scheduled breakfast interview with reporters Wednesday, Schwartz said the Air Force overnight had unearthed the Chu memo. He also said the Air Force determined that no remains from the Shanksville site were handled by the Dover mortuary, "as best we can tell." He added that the Air Force would endeavor to "nail down" with certainty that Dover dealt only with remains from the Pentagon attack.
Schwartz said it was still unclear how many remains portions from the Pentagon were incinerated and dumped in a landfill.
Chu's instructions in March 2002 spelled out how to handle three categories of remains from the Pentagon.
It said those remains that could not be positively associated with an individual, and that were known not to be remains of the hijackers, should be cremated and presented to the superintendent of Arlington National Cemetery for burial. This category also included portions of remains that were positively identified as being from a person whose remains had already been released to that person's family, so long as that family did not want to take possession of the additional portions.
Also, Chu directed that remains positively identified as those of the hijackers be transferred to FBI custody.
The final category described by Chu was those mentioned in the Abizaid report as having been incinerated and placed in a landfill. These remains that could not be identified and were mixed with fragments of "non-biological material."
The dates on which remains in the final category were incinerated and sent to a landfill are unknown thus far.
The Abizaid report included a brief reference to two other memos. One, dated July 25, 2002, appeared to be follow-up correspondence from the acting director of the Army's office of casualty and mortuary affairs about disposing of unidentifiable remains. The other, from an Air Force outfit, was dated Aug. 7, 2002 appears to be a similar follow-up note.