High school students stealing exams

In a town in New Hampshire, about 50 high school students were involved in stealing final exams from their teachers in advanced subjects such as Calculus and Algebra II. I wonder how these students were able to steal the exams. Where is the honor system in terms of cheating? Are the stakes so high that it requires for students to find means of cheating in order to get good grades? I feel that students need to live by a honor system when they are in school. As for me, my exams would never be left in my classroom for sake of students finding them then cheating in my classroom. I will be fair if they are fair to me.