Something Witness does very well is handle exposition dramatically. We need to learn about the different lifestyle of the Amish, and an amateur screenwriter would tell us this is long, boring, expository dialogue.
Here we get our first education through images in the opening sequence of the story. Later we learn more about the Amish in a dramatic context, in which exposition can be sugar-coated like medicine hidden in candy. For example, we learn that the Amish don't have telephones when the John's superior, trying to find out which of hundreds of Amish farms he is hiding out on, reprimands an assistant for not letting his fingers do the walking, calling one farm after another. He is then informed that this would be a great idea - if the Amish had telephones. The dramatic context brings forth this exposition in a natural, dramatic way. Lesser hands would tell us straight out, in dialogue that would be unnatural and serve no purpose other than as exposition.