The Pentagon reopened a decade-old wound on Tuesday, admitting that unidentified partial remains of some victims of the Sept. 11, 2001, attacks were incinerated and dumped in a landfill. "Not only am I broken-hearted, but I am outraged," Diane Horning, whose son died at the World Trade Center, tells The Wall Street Journal. How could such a thing happen? Here's what you should know:

Who is responsible for this?
The blame, according to a government report, falls on the mortuary at Dover Air Force Base. Dover is best known as the place that receives the nation's war dead, but it also handled remains of those killed when a terrorist-hijacked airliner slammed into the Pentagon, as well as some remains from those who died when United Airlines Flight 93 crashed in Shanksville, Pa. (Dover did not handle any remains from the World Trade Center in New York). Dover officials, apparently following instructions from a top Pentagon official, cremated some of the body parts, then gave them to a biomedical waste disposal contractor, which incinerated and dumped them.

How many victims' remains were treated this way?
Nobody can say for sure. Only remains that couldn't be identified — possibly because they were too small, or too charred — were sent to a landfill. When American Airlines Flight 77 crashed into the Pentagon, 184 people were killed, and the remains were sent to Dover. The government report also said that partial remains from some of the 40 people who died in the Shanksville crash were handled in the same way.

Does anyone dispute the findings?
Yes. Lisa Linden, a spokeswoman for the families of United Flight 93, says the Pennsylvania remains never left the control of the local coroner, making the government report "impossible to believe."

Have war dead been treated this way, too?
In at least some cases, yes. The review that uncovered the 9/11 link was ordered by Defense Secretary Leon E. Panetta after mortuary officials were accused of "gross mismanagement" for losing body parts of service members, along with other sloppy and disrespectful practices, including sawing off the protruding arm bone of a dead Marine without notifying his family. Following a Washington Post investigation, the Pentagon revealed last year that it had dumped the incinerated partial remains of at least 274 service members this way between 2003 and 2008, but that doesn't happen any more. Now the ashes are buried at sea.

Sources: CBS News, New York TimesWall Street JournalWashington Post