Washington (CNN) -- Mike McLaughlin knew he buried his father, a veteran of World War I, World War II and the Korean War, at Arlington National Cemetery.
So when he opened the newspaper recently and saw his father's tombstone sunk in the bottom of a shallow, muddy stream, he was stunned.
"At this point, I have somewhere between zero and less than zero confidence in the cemetery's management," said McLaughlin.
As many as 6,600 graves at Arlington Cemetery, the historic and hallowed burial place for fallen U.S. soldiers, may be "unmarked, improperly marked or mislabeled," Sen. Claire McCaskill, D-Missouri, said Thursday.
Cemetery officials had previously estimated just 211 were mislabeled.
The hearing was spurred by Army Secretary John McHugh's June report that revealed 211 graves were misidentified or mislocated. In opening remarks to the subcommittee she chairs, McCaskill suggested the problem might be more widespread.
"At a conservative estimate, 4,900 to 6,600 graves may be unmarked, improperly marked or mislabeled on the cemetery's maps," she said.
McHugh's months-long investigation found "a lack of expertise in contracting processes within the cemetery, coupled with a lack of focused external oversight."
The probe exposed a dysfunctional management team with no oversight, missing documents, poor record keeping and failure to notify next-of-kin about the problems, according to the Inspector General's report.
McHugh said that "by placing everyone in charge, no one was in charge," and vowed to do "everything necessary and possible to right these unimaginable, unacceptable wrongs."
After the investigation, the cemetery's former superintendent, John Metzler, who was scheduled to retire next month, was reprimanded. Metzler's former deputy superintendent, Thurman Higginbotham, was placed on administrative leave pending further review. Both men spoke at Thursday's hearing.
Army Inspector-General Steven Whitcomb said his review found no evidence of deliberate wrongdoing.
But Gina Gray, an Iraq veteran who is suing on grounds that she was fired for bringing the problems to light, wants to see someone held accountable for the blunders. She alleges the cemetery used outdated technology despite receiving millions of dollars to update its record-keeping systems.
"I don't know what it is going to take to get them fired over there," Gray said. "We have evidence of unmarked, mismarked graves, mismanagement going decades back."
McHugh said in June a number of solutions are currently being considered for correctly identifying the remains in question, including exhuming graves for family members to identify their loved ones by the unique caskets containing them, opening the caskets to pick through articles and mementos, or, as a last resort, conducting DNA tests.
Some 330,000 veterans and their family members are buried at the tree-covered and hilly Arlington, Virginia, site overlooking the nation's capital.
McHugh, sworn in as Army secretary in September, has said problems at Arlington Cemetery were allowed to continue as long as they did in part because of fuzzy lines of oversight -- confusion the subcommittee sought to sort through.
"The people who let this happen, whether it was ignorance, incompetence or denial, must be held accountable," said McCaskill.