When I was in basic training during the Vietnam war, one of the drill instructors said that the Viet Cong were completely incompetent and if they shot you, it was because it was a lucky shot. A kid in the back of the platoon then asked, “sergeant, does a lucky shot leave you just as dead as a good one?”
These girls may be just play acting, responding to adolescent peer pressure, have watched one too many scary movies, or any of a number of “excuses” offered by adults. But had they carried out their plot, the victims would be just as dead as if Dracula himself drained them.
I wouldn’t be so quick to try to explain this one away. Normal kids with abnormal ideas, wherever they came from, can be just a deadly as the psychotic serial killer.