I just saw this quite on tumblr:
Were you sober when you wrote “Amy"?
BJ: "I was on heavy medication. I was sober, but I wasn't clear. Seeing how it went down with her - something drew me to write that song. I don't write about people that pass away very often. I think I've done it three times: "X-Kid"; the one about my dad, "Wake Me Up When September Ends" [on American Idiot]; and "Amy." In a weird way, I'm almost desensitized by death, because I learned about it at such an early age. I have this family that is much older than I am, and I have a lot of friends who have committed suicide, gotten into drunk-driving accidents, hung themselves. So death has always been in my life. [Pauses, laughs grimly] That sounds really funny.
But if you look back, I've been writing about addiction forever. There's this other side of me going, "I told you this shit was going down. You wouldn't fucking take it seriously.""