By
Lois Duncan, published in
1978.
One of the relatively few "young adult" books that has left a lasting impression on me. A smooth, charming guy in his 5th year of high school gets flunked--again--by Mr. Griffin, the meanest teacher in school. He convinces a small group of other students to kidnap Mr. Griffin. They don't know that he's got angina, and so when they come back...he's dead.
The book is suspenseful, but its real value is psychological. The main characters are basically OK people who have let themselves get caught up in evil, and are trying to figure out how to get out. At the same time, they find out how limited their own perspectives on other people really are. It made me think, and still does.
This was made into a 1997 TV Movie which I haven't seen. The same author wrote the original book I Know What You Did Last Summer. Please don't hold that against this work.