The activities that could be considered a potential spear phishing scam are:
A courier delivers a duplicate invoice to a business that contains updated payment details of an existing supplier. This could be a way of diverting funds to a fraudulent account by impersonating a legitimate vendor and exploiting the trust relationship between the business and the supplier1.
Payroll receives an external email from an employee looking to update their bank account information. This could be a way of stealing money from the employee or the employer by pretending to be the employee and requesting a change in the payment method or destination2.
An employee receives an email that asks to download an attachment, but the attachment is a malware. This could be a way of infecting the employee's computer or network with malicious software that could compromise sensitive data, disrupt operations, or demand ransom3.
The other options are not necessarily spear phishing scams, although they may be other types of fraud or deception. For example:
An employee receives a phone call requesting that money be sent to assist someone in trouble. This could be a vishing scam, which is a form of voice phishing that uses phone calls to solicit personal or financial information or to request money transfers4.
A business sends its employees an email warning that email passwords must be changed to prevent cyber- fraud. This could be a legitimate security measure, or it could be a phishing scam, which is a form of email phishing that targets a broad audience and tries to trick them into revealing their credentials or clicking on malicious links.
Members of a religious organization receive a donation request by email claiming to be from their leader. This could be a genuine appeal, or it could be a social engineering scam, which is a form of manipulation that exploits the human factor and relies on the victim's emotions, trust, or sympathy.
References:
ACAMS CAMS Certification Video Training Course - Exam-Labs3
Exam CAMS: Certified Anti-Money Laundering Specialist (the 6th edition)4 ACAMS Study Guide for the Certification Examination, 6th Edition, Chapter 3, page 53: https://www.acams.
org/wp-content/uploads/2019/08/ACAMS-Study-Guide-6th-Edition-Chapter-3.pdf ACAMS Study Guide for the Certification Examination, 6th Edition, Chapter 3, page 54: https://www.acams.
org/wp-content/uploads/2019/08/ACAMS-Study-Guide-6th-Edition-Chapter-3.pdf ACAMS Study Guide for the Certification Examination, 6th Edition, Chapter 3, page 55: https://www.acams.
org/wp-content/uploads/2019/08/ACAMS-Study-Guide-6th-Edition-Chapter-3.pdf ACAMS Study Guide for the Certification Examination, 6th Edition, Chapter 3, page 56: https://www.acams.
org/wp-content/uploads/2019/08/ACAMS-Study-Guide-6th-Edition-Chapter-3.pdf

The bank should request a formal letter be submitted to verify the validity of the request, as this is the best practice to ensure compliance with the law and protect customer privacy. The bank should not confirm or deny the existence of a customer relationship, nor provide any information without proper authorization. The bank should also not inform the board of directors before responding to the request, as this could compromise the confidentiality of the investigation or alert the customer.
References:
* ACAMS CAMS Certification Video Training Course, Module 2: Compliance Standards for Anti- Money Laundering (AML) and Combating the Financing of Terrorism (CFT), Section 2.3: Data Protection and Privacy, Slide 10
* ACAMS CAMS Certification Study Guide, 6th Edition, Chapter 2: Compliance Standards for Anti- Money Laundering (AML) and Combating the Financing of Terrorism (CFT), Page 51 Reference: https://ico.org.uk/for-organisations/guide-to-freedom-of-information/receiving-a-request/

According to the CAMS Study Guide, page 191, "Reloadable open-loop prepaid cards are a high-risk product for money laundering because they can be used to store and move large amounts of funds anonymously. They can also be used to access cash at ATMs or through cash-back transactions at merchants." Therefore, option B is a red flag that may indicate money laundering, as a non-bank customer who regularly loads large amounts of cash onto several prepaid cards may be trying to avoid identification, verification, or transaction reporting requirements.
References:
CAMS Study Guide, page 1911

The compliance officer should provide a high level summary of the activity and the interactions with law enforcement to the board of directors, as this would be the most appropriate way to escalate the information without compromising the confidentiality of the STR or the ongoing investigation. Providing a copy of the STR or the letter from law enforcement could expose the bank to legal risks or jeopardize the investigation.
Informing the regulator to bring it up with the board would not be sufficient, as the compliance officer has the responsibility to report directly to the board on significant compliance issues.
References:
* ACAMS CAMS Certification Video Training Course, Module 5: Risk Management, Lesson 5.3:
Reporting to Senior Management and the Board1
* ACAMS CAMS Certification Study Guide, 6th Edition, Chapter 5: Risk Management, Section 5.3:
Reporting to Senior Management and the Board2