Exam IIA-CIA-Part2 topic 1 question 89 discussion

During an audit of a retail organization, an internal auditor found a scheme in which the warehouse director and the purchasing agent diverted approximately
$500,000 of goods to their own warehouse, then sold the goods to third parties. The fraud was not found earlier since the warehouse director updated the perpetual inventory records and then forwarded receiving reports to the accounts payable department for processing. Which of the following procedures would have most likely led to the discovery of the missing materials and the fraud?