Structured transactions are a common method of money laundering, where large amounts of cash are broken down into smaller deposits or withdrawals to avoid reporting thresholds or detection. The most effective tool to detect such transactions is a software program that can link apparently unrelated transactions by using various criteria, such as customer name, address, account number, identification number, transaction amount, date, time, location, etc. Such a program can help identify patterns, trends, and anomalies that may indicate money laundering activity.
References:
ACAMS CAMS Certification Study Guide1, Chapter 2: Money Laundering Risks and Methods, Section
2.2: Common Money Laundering Methods, pp. 51-52
ACAMS CAMS Certification Video Training Course2, Module 2: Money Laundering Risks and Methods, Lesson 2.2: Common Money Laundering Methods ACAMS CAMS Certification Exam Outline3, Domain 2: Compliance Standards for Anti-Money Laundering (AML) and Combating the Financing of Terrorism (CFT), Task 2.2: Implement risk-based CDD, EDD and ongoing due diligence policies, procedures and processes, p. 13

The correct answer is C, as mapping scenarios are helpful in mitigating the weakness of not generating alerts when activity is consistently abnormal over a long period of time. Mapping scenarios are used to compare a customer's activity with their expected activity based on their profile, risk rating, or historical behavior1. By using mapping scenarios, the organization can identify customers whose activity deviates significantly from their normal or expected patterns, and flag them for further investigation. Mapping scenarios can also help detect changes in customer behavior over time, and alert the organization of any potential money laundering or terrorist financing risks.
References: 1: AML Scenarios: Transaction Monitoring Challenges - Unit21, page 1.

A significant reduction in suspicious transaction report (STR) filings at a particular branch could indicate that the branch is not properly identifying and reporting suspicious activities, or that the branch is experiencing a change in customer behavior or risk profile. Therefore, the most appropriate action for an anti-money laundering specialist is to review the branch exception reports, which are reports that highlight transactions or activities that deviate from the expected or normal patterns, based on the customer profiles and risk assessments. By reviewing the branch exception reports, the specialist can determine whether there are any changes in activity that warrant further investigation or reporting, or whether there are any gaps or weaknesses in the branch's compliance program or procedures.
The other options are not as appropriate as reviewing the branch exception reports, as they do not directly address the issue of suspicious activity reporting. Placing the branch on the watchlist may be a subsequent action, but it does not provide immediate insight into the reason for the reduction in STR filings. Analyzing the branch activity reports may show whether there has been a decrease in branch activity, but it does not explain why the activity has decreased, or whether the remaining activity is suspicious or not. Reviewing the staff records may reveal whether inexperienced personnel are in critical positions without appropriate training, but it does not account for other factors that may affect the branch's compliance performance, such as management oversight, internal controls, or customer risk.
References: ACAMS CAMS Certification Study Guide (6th edition), page 361; ACAMS CAMS Certification Video Training Course, Module 2, Lesson 12; What Is a Suspicious Activity Report (SAR)? Triggers and Filing3; Reporting suspicious transactions to FINTRAC4.

Explanation
Under the Wolfsberg Correspondent Banking Principles, conducting enhanced due diligence (EDD) is an obligation for correspondent banking clients that present greater risks. This may include conducting additional research and analysis of the client's background, ownership structure, and transactions. EDD may also involve obtaining additional documentation, verifying the client's identity, and conducting periodic reviews to ensure ongoing compliance. The level of EDD required should be commensurate with the level of risk posed by the correspondent banking relationship. Therefore, option B and D are incorrect. Option A is not specific enough to address the question. Option C is the correct answer as it highlights the importance of senior management approval for high-risk relationships, which is a key component of EDD.
Reference: Certified Anti-Money Laundering Specialist (the 6th edition) Study Guide, Chapter 7, page 12.
Wolfsberg Correspondent Banking Principles (2014)