1) We do not have access to the full case at this point. What lead to the discovery of the material by the teacher. If this student said anything, or communicated non-verbally, for example that indicated a threat and lead to the discovery. Or if he had the book in question open in class or another public display of it. *shrug*
2) The alleged physical actions taken to assembling the bombs, if accepted as such by judge/jury, would demonstrate his intent and an attempt at the assault where-upon his legal goose is cooked.