"Ransom," who knew of JR in some way, and getting the idea of a copycat crime---as a joke, to stir things up for excitement, and then sit back and watch while the police and Ramseys tried to figure out who did it. A joke that wasn't suppose to end in murder. Getting fast cash may have been part of it, with the thought no police would be called, and they'd get away with it, and they'd leave JBR someplace alive....all before noon the next day.

I can also see someone of foreign distraction, where English is not his first language, using the movie lines thinking they would scare the Ramseys enough to not call the police.

I can also see a feminine quality in the note, because it's so wordy, and 2/3's of it is polite....with perhaps the end being dictated. There is definitely a change of mood towards the end---almost like someone else's words.

'Course a paranoid schizo that talks to cookies, is beyond my comprehension---you'd think someone like that would crack at some point, and the voices would tell him to confess.