I thought the opening of the book was very effective because it illustrated the closeness of this principal and his students. This was a happy school. There was a sense of community and bonds of trust between the students, faculty and staff. What Mr. DeAngelis was worried about was the danger of drinking and driving, which is a very familiar threat. They're about to have a prom. It's an ordinary setting. We know what will happen, but we understand how people in the school and the community could feel secure that such an event would never occur there, even though they read stories about the increase in school shootings.
Jumping to Q. 6, the next chapter illustrates the same "ordinariness" in the appearance of the killers. They worked in a pizza place, had relationships with girls, had friends. Eric, usually successful in picking up girls, was trying to get a date for the prom. Dylan was going with a nice girl, sharing a limo with five other couples. Eric was a good student; Dylan was very smart but unreliable, had a problem with his temper. Nevertheless, he wasn't disturbingly different. They participated in extracurricular activities, were baseball fans and belonged to a bowling league. They drank some, but weren't seen as "problem" drinkers; they didn't do drugs. They liked math and computers, played video games, made videos.
In hindsight there were many red flags; if all of the information had been collected in one place and available to an adult or adults, including the content of Eric's website, threats they had made, their contact with the legal system, and things their friends had heard and seen, there would have been alarm and action. They weren't showing the red flags associated with school shooters, however: they weren't friendless loners who were failing in school and getting high all the time. They hadn't been bullied; in fact, they were bullying younger kids. They didn't come from broken homes, had no history of abuse. No one who didn't have access to most or all of the pieces would have picked them out--they didn't fit the profile.