Is it more natural to saying "peer" than "co-worker" among the organisations like polices, firefighter and so on?
Both are very natural and commonly used. Using "peers" implies that someone is at the same level or position as another. This can also be used in everyday situations; not just in a work setting. A "coworker" can be anyone you work with regardless of position. In this video, Ray and Rosa are in higher job positions than the police officers. He may have used "peers" because the officers that seen Deetmore humiliated by Rosa are at the same occupation level as him. Here are some examples of "coworker" and "peer" being used. Ex: He is a coworker of mine. Ex: We used to be coworkers at Aldis. Ex: She is my peer at university. Ex: You humiliated me in front of my peers at school.