For best investigative results, travel fraud audits should be performed by an employer on at least a yearly basis if possible.  The reason for this is that major hotels routinely purge their systems on a 6-month to yearly basis, so it can be difficult for an investigator to obtain detailed hotel expense information after a year.

This problem came up for me recently when asked to conduct an audit of travel expenses going back several years.  In instances where the employee had submitted a non-itemized hotel receipt more than a year prior to the investigation, it was difficult to ascertain whether the employee had made fraudulent or padded hotel charges, including exorbitant hotel restaurant charges.  Whereas more recent itemized hotel receipts could be obtained and they revealed meals for a spouse, children, and other guests at the hotel restaurant and excessive alcohol charges.  Further, the itemized hotel receipts showed that meal expenses were charged to the hotel bill (which the employer reimbursed) even though the employee requested money back for the same meal in a separate entry on the expense report, and even though the employee had also received an advance "per diem" payment prior to the business trip to cover meals.  In this case, the employee was obtaining a triple recovery for the same meal!

I recently heard a story about an employee somehow obtaining a handful of blank receipts from a restaurant and subsequently handing them out to co-workers who needed forms to submit expense receipts for meals.  Employees have also been known to alter a duplicate copy of a receipt and change the document number, or change the dollar amount, for example, changing a "1" to a "4" or "7", or adding an extra digit to the front of an existing number, or cutting off the top the business name or logo of a document to hide an irregularity. 

Another scam is to charge the employer for coach or business class airplane fare (on an expense receipt or using a company P-Card), obtain a refund on the ticket, then purchase a super-saver ticket for the same flight, and pocket the difference.  Or worse, booking a trip and getting reimbursed for it by the employer, getting a refund from the airline, and not traveling at all.  Or, an employee might claim he is attending a conference out of state, but then the meal receipts he submits (which are sometimes time-stamped by restaurants) reflect that he was dining in the middle of the day at location miles away from the business conference he was supposedly attending.  In these types of cases, an employee has essentially received a full paid vacation out of town (free airfare, free hotel, free meals, plus salary) and is skipping the conference.  

In sum, a strong monthly review and periodic audit process are essential to circumvent travel reimbursement fraud by employees.