The youngsters were found with knives at Bartow Middle School in Florida on Tuesday, and were arrested.
The girls, who have not been named, are said to have been found in a bathroom holding a goblet meant to hold the blood of their victims, and are also accused of planning to kill themselves after the bloodbath.
Two middle-school girls - ages 11 and 12 - brought knives to their Florida school in a foiled plot to kill classmates, cut them up and drink their blood before killing themselves, police officials said Wednesday.
Bartow Middle School administrators "saved" the school from the girls' freaky scheme when the duo's absence from class triggered a search.
When asked about motivation, the girls reportedly told police that they were Satan worshipers. According to FOX 13, authorities discovered a hand-drawn map of the school with the words "Go to kill in the bathroom" written on it.
An assistant principal found the two girls hiding in a bathroom with a goblet, Mr Hall said.
Afterwards, the girls would leave the body parts at the school's entrance before killing themselves, they said.
The girls, who remain locked up, were charged with "conspiracy to commit murder, possession of a weapon on school property, and disrupting a school campus".
The two girls allegedly told officers they wanted to kill at least 15 people.
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There was already an increased police presence at the school following a tip-off from another student about a rumour to a a possible threat to students.
"This is horrific, and if I had children in school I'd be scared half to death", Hall admitted.
Some of the weapons the girls planned to use included butcher knives, paring knives, and a pizza cutter.
Byrd credited staff at Bartow Middle School for following correct procedures that led to the discovery of the murder plot. According to authorities, the girls planned to wait there and corner potential victims, WFTS reports.
"I don't think either one of them was a ringleader", he added.
The girls, 11 and 12 years old, planned, among other acts, to drink the blood of their victims from a goblet, according to investigators.
Officials with Polk County Schools said extra police officers and guidance counsellors would be at the school this week.
Reportedly, the school's vice principal found the girls in the bathroom before anyone was harmed after one of the girls was reported missing from her classroom.