Howard University journalism professor James Rada says NBC "found itself in a no-win situation" and that releasing parts of the killer's diatribe was the right move. He noted that the Unabomber wasn't caught until after his mainfesto was released and people recognized his writings.
It occurs to me that gun control is a lot like DRM. Both frustrate the intentions of the law abiding, but are easily circumvented by the criminally inclined. So why do I support one but not the other? Well, because I'm generally in favour of people being able to enjoy the music and video that they have purchased where they like, when they like and how they like. I'm less inclined to encourage them to take the same attitude towards AK47s that I advocate for MP3s.