Final answer:
The first officer at the scene of a bank robbery should wait for backup before entering the building, ensuring their safety and that of potential victims and bystanders.
Step-by-step explanation:
When a police officer first arrives on the scene of a potential ongoing crime and backup has not yet arrived, the safest and most tactically sound option is for the officer to assess the situation from a secure position and wait for additional support. This ensures not only the safety of the officer but also the potential victims and bystanders. In this case, the most appropriate action would be: a. Wait for backup, then carefully enter the building with at least one other officer.
In a situation where a crime is possibly still in progress, such as a bank robbery, the initial responding officer's primary concerns are to secure the area and ensure public safety, which is why immediate entry could be hazardous and counterproductive without a clear understanding of the threat level or the status inside the building. By waiting for backup, the officer can devise a more strategic approach with additional resources, which can include setting up a perimeter, evacuating nearby areas if necessary, and communicating with dispatch about the situation.