OTTAWA - The prime minister's mail room has lost some historical documents on sports, music and politics -- and the material appears to have been accidentally shredded.

The package of six documents arrived in the busy mail facility last May 5. The envelop was date-stamped as being received but it was not tracked as required, and the material soon disappeared.

Mail room supervisors were not even aware of the loss until they received a registered letter from the sender on July 4 asking for confirmation that the gift of memorabilia to the prime minister had arrived safely.

A search was launched in the mail room, at the prime minister's office in the Centre Block of Parliament Hill, and at 24 Sussex Drive, Stephen Harper's official residence. Staff were interviewed, but the missing documents never surfaced.

An internal government investigator was finally brought in on Oct. 7, and eventually concluded "there was no indication that the items were taken by any member of the staff."

"Given the large volume of mail that was processed in early May following the election, it is possible that the package was accidentally discarded into the ... waste bin and shredded."

Information related to the Case of the Missing Memorabilia was provided to The Canadian Press under the Access to Information Act.

Released versions of memos to Stephen Harper from last December carefully black out the identity of the donor and the contents of the AWOL documents, to protect privacy.

A spokesman for the Privy Council Office, the prime minister's own department, declined to provide further details.

The mail room was swamped with almost 96,000 pieces of mail in May last year, after the May 2 federal election produced a Conservative majority. That's almost three times the average monthly flow of 35,000 pieces in each of the first four months.

Harper wrote to the sender in December to thank him for the package "and to express his regret for the loss of the items," said Privy Council Office spokesman Raymond Rivet.

"There was also a written apology from PCO, which was responsible for handling the correspondence."

The sender was not compensated for the loss, nor was any dollar value determined for the missing material, Rivet added.

The embarrassing incident exposed a flaw in mail-room processing, prompting changes. Staff must now put their initials on all registered mail they receive, and any documents destined for the shredder must first be inspected by a supervisor.

While the exact nature of the lost documents has not been released, the topics -- sports, music and politics -- are favourites of Canada's prime minister, who is publishing a hockey history book and has played old Beatles tunes on piano in public venues.

The Harper government has also promoted Canadian history, recently funding commemorations of the obscure War of 1812.