Anyone absolutely at anytime can be converted into an agent as needed. If someone dies in the dream world of the matrix then they die in reality as well. The body can not exist when the mind belives that it is dead. They are in search of their former leader who is in the Matrix as agents attempt to extract information from him. The heros arrive at a major complex in the dream world of the Matrix.
Guards are everywhere as are metal detectors.
Guards run a metal detector over them and it goes off instantly. Keanu Reeves lifts his overcoat and reveals a multitude of weapons. Fighting his way in through hundreds of guards, kicking off walls and people. These real human beings in the Matrix have learned a bit about manipulating the programs the machines are controlled by. In the movie's end agents are finally able to be killed and Keena Reeves realizes that he is the chosen one meant to awaken man from his dream state.