OTTAWA - Someone has helped themselves to a few choice specimens from the Bank of Canada's currency museum, newly released documents show.

Red-faced bank officials are short about $16,700 following the unsolved theft at the central bank's popular tourist attraction.

"There is no plausible explanation for the discrepancy other than theft," says an internal audit obtained by The Canadian Press under the Access to Information Act.

"The procedures for note holdings should have been stronger . . . some of the procedures that did exist were not followed."

The missing money came not from the display cases, but disappeared from a stash of cash the museum uses to help teach visitors about counterfeit currency.

The so-called note exchange program allowed patrons to swap their old-style bills for new-series money with special security features designed to thwart counterfeiters. The popular program, created in 2001, has been abruptly cancelled in the wake of the currency caper.

Bank officials first noticed money was missing in June last year, but took five months to complete an audit and call in the Ottawa police, internal documents show.

Asked why the process took so long, bank spokesman Christian Vezeau said only that "we conducted a thorough internal investigation through which we were able to rule out any accounting errors and we concluded that the money was stolen."

Det. Tracey Turpin of the Ottawa police said the case is now considered closed, partly because the bank complained long after the alleged theft.

"A lot of time had passed and just about everybody that had worked at the time had moved on," Turpin said in an interview. "To track who was working when, when the money would have gone missing, was virtually impossible."

The police did not conduct any interviews. But the Bank of Canada's own investigation suggested it was an inside job because the money went missing in an area accessible only to employees, Turpin said.

Vezeau declined to say whether any staff members have been disciplined or fired, citing privacy rules.

He added: "The procedures in place for the storage, handling and regular counting of the money for the boutique till were further tightened when the museum became aware of the shortage."

The currency museum, which attracts 35,000 visitors a year, is nestled inside the original 1934 Bank of Canada building, which itself is embedded inside the bank's modern glass-and-steel towers near Parliament Hill.

Opened in 1980, the modest facility costs about $1.5 million a year to operate, with 20 full-time staff. There's no admission charge and guided tours are free. The galleries feature coins and currency from around the world, with an emphasis on Canadian money.

The internal audit, dated November last year, noted that "high staff turnover" was partly responsible for the lax security that apparently allowed the theft. "Management oversight in such an environment should have been stronger," it said.

The heist at headquarters is not the first time the central bank - which prides itself on tight security - has seen its assets go AWOL.

In 2004, a bank employee was fired and charged with theft after $10,000 was stolen from a Toronto bank-note facility, where large bundles of cash are received from chartered banks.

And in 2001, the central bank lost track of $1 million worth of $1,000 notes at an Ottawa-area shredding facility. An exhaustive internal investigation found that "misappropriation of bank notes cannot be conclusively ruled out," and a new security camera system was installed.