The Dark Knight question?

During the hospital scene, when the cop is next to the bus and he says something like . . . "We have everyone out of the hospital," and then he says, "Davis!" and he starts to run into the hospital. And he just keeps saying Davis down the hospital hall, and then he goes into Harvey's room, and the Joker shoots him. Well, who is Davis? and why did he walk into Harvey's room saying that? I might be thinking to hard about this but it has been bugging me! Thanks in advance!