Well...
It was well animated by a kid who never had the chance to mature as an artist. Was this a sign that he was going to shoot a bunch of people and then off himself? I don't think so.
Is it common for smackheads to start by smoking weed? Sure. Doesn't mean smoking weed is a sign. There's a huge matrix of steps to take to get to any point in your life, and being stupid and emotional (as well as being a pothead) is one of the bottom rungs, just above being born. After all you need to be human to be able to shoot people in the first place. Maybe that was a sign.
By the way (for you lamens), I'm just using the weed and heroine thing as a metaphore for this film and his actions.
This was an expression of emotion. Do content and happy people kill others? Not very often. But that doesn't mean someone who's pissed off is going to kill anyone. It's no suprise that a kid that screwed up animated something like this, but in reality this could have been done by any emotional kid. I'd be suprised if kids didn't express themselves. Then again, this did seem a bit mindless.
In my opinion everyone is capable of anything. It just depends what you adopt to be your morals, what you are taught to be your morals, and how far you are pushed. Then again some people are born screwed up, some aren't.
It sucks that he shot a bunch of people, including himself, but he deserves neither damnation or empathy. He's just another stupid kid who went down another stupid path in the big stupid web of possibilities.
Anyway, it's not like people haven't been killing eachother since the beginning of... yunno, whenever it began. I just find it interesting that these kids are killing people in something other than the name of God. Kinda refreshing.