The Transportation Security Administration’s (TSA) methods for classifying its Office of Inspection (OOI) criminal investigators as law enforcement officers were adequate and valid, but the data TSA used were not adequate or valid. TSA’s criminal investigators spend at least 50 percent of their time performing criminal investigative duties to be classified as law enforcement officers. The FY 2017 timesheet data TSA used to validate that its criminal investigators met the 50 percent requirement were not adequate and valid as the data were not always timely submitted and approved. This occurred because OOI officials lacked oversight and accountability for the timesheet submission, review, and approval processes. Further, criminal investigators and their supervisors did not always complete and approve certification forms as required to verify eligibility for premium pay. In some instances, incorrect timesheet calculations inflated the annual average of unscheduled duty hours criminal investigators worked to be eligible for premium pay. OOI management did not develop and implement guidance to review these key calculations annually. Without better oversight and valid timesheet data, TSA cannot ensure it is accurately classifying criminal investigators as law enforcement officers. TSA also may be wasting agency funds on criminal investigators ineligible to receive premium pay. We made four recommendations that, when implemented, should help TSA improve data used to classify its OOI criminal investigators as law enforcement officers. TSA concurred with all of our recommendations.