Matrix Agents Rules

There’s one thing about both Matrix movies that I’m still confused about. When is it that Agents are able to inhabit other people? At times, it seems like they can inhabit anyone. Like, in the last chase scene in The Matrix, random people keep turning into Agents, also that homeless guy. In the car chase sequence in Reloaded, people keep turning into Agents. So can they inhabit anyone? Why then in the Matrix do they not take over the police officers in the beginning of the movie when they’re fighting Trinity? They do take over them later in the movie. Why not in the beginning? I dunno, that doesn’t make sense to me.