Which of the following is a method of surveillance?

The method of surveillance defined in the question involves observing and gathering information about individuals or activities, typically to monitor behavior or movements. Moving surveillance of a vehicle and/or person is a classic example of active surveillance techniques. This method allows for real-time tracking and observation, providing law enforcement or investigators with critical insights about the individual or vehicle's actions, routes, and patterns.

In contrast, the other options do not primarily focus on surveillance. Public interviews of suspects involve directly questioning individuals, which is more about information gathering through interaction. Mobile tracking of financial accounts, while a form of monitoring, does not involve physical surveillance of people or vehicles but rather focuses on digital footprints. Similarly, collecting written statements from witnesses is an evidential gathering process instead of surveillance, as it does not involve real-time monitoring or observation of behavior. Thus, the correct approach that aligns with traditional definitions of surveillance is the moving surveillance of a vehicle and/or person.