During an interview, Alex asked a fraud suspect if he could retrieve the suspect's account...

Fraud examiners can obtain documentary evidence by consent, subpoena, or other legal means. While oral consent may sometimes be sufficient, bank records from financial institutions generally require written consent. Without written consent, the bank is not required to provide access. As stated in the manual:

“Accessing a subject’s bank records from financial institutions, for instance, generally requires written consent. If no consent is given… legal action might be required, most often a subpoena or other court order”.

Thus, although the suspect gave oral consent, Alex cannot access the bank records without written authorization or legal order.