WASHINGTON — The Army has launched a criminal investigation after Arlington National Cemetery officials found eight sets of cremated remains buried in a single grave with a headstone marked "unknown."

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Cemetery spokeswoman Kaitlin Horst says officials learned of the problem in October and that investigators have now identified three of the sets of remains and are notifying those families.

One set could not be identified and was reburied, and investigators are still working to identify the others.

The probe comes on top of a report earlier this year that found more than 200 graves had been mismarked on cemetery maps.

Christopher Grey, a spokesman for the Army Criminal Investigation Command, said that while those previous problems might have been human error, the placement of eight urns in one grave was unlikely to be by mistake.

"Unknown" is "not likely a mistake," the Washington Post reported Grey as saying. "It demanded an investigation to determine if there's any criminality involved in the burials."