[LuvablePsycho]

Originally Posted by Sculpt

Yep, only Halloween (1978) and Halloween II (1982) are one story, both scripts written by Carpenter and Debra Hill, and they ended the story. I personally wouldn't even bother thinking about the rest of "the series" which are written by other people. But in the original story I think the "sister thing" is very interesting. I mean, this little independent film, Halloween (1978), sure grabbed the attention of the USA in 1979... seemed to strike a nerve. Most film critics give it 4/4 stars. It has some distinction.

No, I don't think the film ever explains why he killed his sister in the first place. I don't know if Carpenter or Hill have ever explained it.

Sometimes someone makes an art piece, and then people try to figure it out afterward, often looking for subconscious reasoning.

Towards that end, since you asked, I'd go out on a limb and say the 60's-70's brought a "free-love sexual revolution", and there seems to be an instinctive protective nature in fathers and brothers to protect their daughters/sisters in this area... protect them from harm, unmarried pregnancy, their reputation, the family reputation, etc. Maybe "the Shape", as Carpenter artfully calls the murderous supernatural being inhabiting Michael, is a symbol of this male-family protective/punitive instinct against premarital sex of the daughter/sister. I'm sure I'm not the first to suggest this.

I was being half-sarcastic about what I said but I think I might have some kind of point. He was a little boy and it was his own sister he was witnessing having sex, so maybe it was traumatic for him to see his own sister in that situation? Of course I doubt most normal kids would ever murder their own sister just for that so he may have had some kind of underlying psychological problem and the trauma of seeing his own sister in that situation caused him to snap.