COLUMBIA, Mo. -- The Missouri senator whose subcommittee is investigating potential contracting fraud at Arlington National Cemetery on Monday said the number of mislabeled graves there could be in the thousands.

An internal Army investigation found at least 211 discrepancies between burial maps and grave sites at Arlington. The review found lax management of the cemetery and a reliance on paper records to manage the burial sites.

At a news conference Monday in Columbia, Democratic Sen. Claire McCaskill said the number of burial site errors could be much higher because the Army report was limited to a small section of the cemetery.

McCaskill called the growing scandal a matter of "heartbreaking incompetence" and said the military has spent more than $5.5 million over seven years in its unsuccessful attempts to computerize the cemetery's burial records.

"At the very essence here you have waste," she said. "There may be fraud - we don't know at this point."

The Senate Homeland Security and Governmental Affairs' subcommittee on contracting oversight, chaired by McCaskill, will hold a hearing in Washington on Thursday on its cemetery investigation.

The list of invited witnesses includes former cemetery superintendent John Metzler and deputy superintendent Thurman Higginbotham. Both retired earlier this month after they were forced to resign, and McCaskill said she is not certain if either will show up to the hearing. She declined to say whether the subcommittee would subpoena either man.

"We are doing everything we can to get both (of the officials) to the hearing," she said. "Their attendance is not a certainty."

Robert Mance, Higginbotham's Washington lawyer, did not immediately return a telephone call seeking comment. And an Arlington cemetery spokeswoman declined a request for comment, noting that Army leaders "will provide insight" on Thursday.

Perched along the Potomac River across from the nation's capital, Arlington National Cemetery is considered among the country's most revered burial sites, with more than 300,000 people interred with military honors. An average of 30 funerals occur each day.

The cemetery includes the graves of former presidents as well as U.S. Supreme Court justices.