DENVER -- Denver police are investigating the embezzlement of $170,000 from Denver International Airport taxi fees.

A search warrant obtained by 7NEWS shows the scam went undetected for nearly two years.

At least 16 cash collections made by DIA Ground Transportation Department workers between November 2007 and late June 2009 vanished en route from that agency to the airport finance department without making it to the bank.

The probe was triggered when a random DIA internal audit found a $10,000 collection missing in June, sources told 7News. Police said they were alerted about the possible theft on Aug. 28.

Investigators obtained a warrant on Oct. 7 to search the Denver Community Credit Union account of a DIA Finance Department cashier "who is believed to be the last person to have handled the funds in question," police Detective David Stolley wrote in an application for the warrant.

In fact, the clerk, a 47-year-old Adams County woman, told 7NEWS in a Wednesday phone interview that she remains on the job and has been interviewed by police.

"I have been told by my superiors not to talk to anyone about it. So I really don't feel comfortable talking to you about it," said the woman, who referred 7NEWS to her manager and hung up the phone. She did not appear to consider herself a suspect.

7NEWS is not identifying the woman because she has not been arrested nor identified as a suspect.

DIA officials want to find the problem and fix it.

"It is a lot of money. And of course we're embarrassed," said DIA spokesman Chuck Cannon. "We're...more concerned, I think, than embarrassed. Because we want to find out if we’ve got an issue, we want to fix the issue. If we have a weak spot in our accounting system or our cash-management system, we want to find that and fix it."

“We have a number of checks and balances. You know, two people have to sign, two people have to count the money and all of this," he added. "Part of what we hope the investigation will show us is if there are weak spots in that, how can we make them better and fix them so it can’t happen again.”

Denver police spokesman Loretta Beauvais confirmed there is "an active ongoing investigation. So, no suspects are being named and there's been no arrests."

Beauvais said there's an "undetermined amount of money" missing. But the search warrant affidavit states, "At this time, $170,366.55 in cash deposits is unaccounted for."

It's unclear if the embezzlement scandal played a role in the suspension of DIA Chief Financial Officer Stan Koniz, who was placed on investigatory leave Thursday by Airport Manager Kim Day.

Koniz told The Denver Post that Day cited insubordination, lack of collaboration and an overstepping of his authority among the reasons for her action.

"None of it is true," said Koniz, referring to insubordination accusations.

The missing money comes from a $3.50 fee taxi drivers pay into vending machines for tokens required to exit a holding lot and pick up airport customers. Cabbies told 7NEWS they can only pay for the tokens with cash -- not credit or debit cards. The $3.50 fee is passed onto cab patrons in fares, the drivers said.

Ground Transportation workers remove the cash from the vending machines, count it, and log the amount and deliver it to the finance cashier, according to the search warrant.

The 16 missing cash collections -- each containing about $10,000 -- were "documented in a log as being counted, collected and delivered" to the finance clerk, the warrant stated. "Ground Transportation found that there are no corresponding deposit slips or records from Finance showing these funds were deposited into the bank."

The finance cashier is supposed to give the deposits to armored-car couriers who deliver it to the bank.

"The reported thefts occurred after (the woman cashier) was assigned the duties of account clerk at Finance," the warrant stated.

The woman cashier attracted suspicion because she declined to take a lie-detector test, while some ground transportation workers did take the tests, sources told 7NEWS.

It is unclear whether someone could have falsified the cash collection logs to indicate that the money was delivered to the cashier -- and throw suspicion on someone else.

Since the thefts, the airport has beefed up oversight by having three ground transportation workers collect money from the token machines, sources told 7NEWS.

The City Auditor's Office learned of the DIA embezzlement when 7NEWS contacted the independent watchdog agency.

"The potential theft of $170,000 is very troubling," said Denis Berckefeldt, spokesman for the auditor's office. "We always stress to agencies to make certain that appropriate and stringent internal controls are in place to ensure that money is always accounted for."

"There's fiscal rules in the city that require that cash be deposited daily" and that the deposit is verified, he said. If the money can't be deposited for an unusual reason, it must be secured in a safe, he added.

"There should also be at least two sets of eyes verifying that the money is properly collected and deposited," Berckefeldt said. "Appropriate internal controls should ensure that any discrepancies will be discovered immediately and large-scale theft cannot occur."