Corrected entry: After Heather Chandler is killed, shouldn't there have been some work done in the house involving an investigation? You would think that Veronica's and JD's fingerprints would have been all over the place, considering neither of them were wearing gloves.
Question: Why did JD expect anyone to believe his plan for the bomb at school - that all of the students signed a mass suicide note? Nobody would think that so many people, with different personalities and interests, agreed to die together. He later tells Veronica, "Pretend I did blow up the school, all the schools" - implying that he wanted to do this again. He might be crazy, but he was careful in how he executed the murders of Heather, Kurt, and Ram. Why the ridiculous bomb plan?
Answer: He doesn't care if anyone believes it or not; he is trying to make a statement about society and that no matter how we see ourselves in life, we are all the same when we're dead.
Answer: The students didn't know they were signing a "mass suicide" pact. They thought it was a petition to win a free concert from a popular band. JD covered the suicide wording on the paper with a sticker that made it look like a contest entry. He pulls off the sticker and reads the real message after he finds Veronica hanging in her room.
That was not the question. It's a question of why JD thinks anyone will believe the note, after all the students are dead. Has nothing to do with the students knowing what they were signing.
Plot hole: Three gunshots were fired for Kurt and Ram's "double suicide" and almost two minutes pass between shots 2 and 3. Doubtful two police officers could think they shot each other.
Suggested correction: An officer could think that one boy shot the other twice, killing him with the second bullet, before that boy was successful in killing him. The remaining boy would then kill himself. "Shot each other" might be a sloppy description, but basically, Kurt and Ram are both dead. There is a letter - forged by Veronica - which "reveals" that they were a couple. No signs of anyone else being involved. The police consider it a "double suicide" because they believe the letter.
Interesting theory, but I respectfully disagree with your correction. Three gunshots to two dead bodies, each with one bullet wound, would arouse suspicion despite what a letter found at the scene says. If one of the boys killed himself, there would be some evidence to support that such as powder burns around the wound or powder residue on his hands. In fact, a forensic scientist would have performed a GSR test on the hands of the shooters to confirm they did in fact fire the weapons.
Correction: The coroner ruled it a suicide so the police have nothing to investigate.
jle
Yes, the coroner ruled it a suicide. The investigation takes place before that: immediately when the body is found.