Thank you for the opportunity to help you with your question!
yes!...............the auditor has the responsibility to search for fraud but cannot find in every case because he is not mandated to do investigations concerning the fraud,only including it in the reports and recommend for steps the company may take to curb it.
'The primary goal of external auditing is to determine the extent to which the organization adheres to managerial policies, procedures, and requirements'
Please let me know if you need any clarification. I'm always happy to answer your questions.