A 14-year-old girl was charged Wednesday with first-degree murder in the death of an 11-year-old girl who was stabbed more than 30 times at the suburban Chicago home where they both lived.

During a court hearing Wednesday, prosecutors said the suspect told authorities the 11-year-old didn't appreciate all she had done for her, including making dinner and doing the younger girl's chores. Authorities haven't released the names of the victim or the suspect, nor have they said how the two are related.

Dr. Thomas Rudd, the county's coroner, said the victim died of "multiple sharp force injuries." He said the girl had stab wounds to her face, neck, chest and arms, and that two stab wounds penetrated her upper left lung. He also said there were indications that the younger girl fought for her life, including defensive wounds on her left hand that indicated she "probably grabbed the knife" and a defensive wound on her right thumb.

Rudd said police recovered the knife believed to have been used in the attack and that judging from the injuries. It's about 4 inches long.

Lake County State's Attorney Michael Nerheim said a juvenile court judge approved the first-degree murder charge against the older girl during Wednesday's juvenile court hearing. A state's attorney spokeswoman said the suspect was being held in a juvenile detention center.

Mundelein police Chief Eric Guenther said the older girl called 911 after the attack and was arrested after police found the victim's body on a bedroom floor.

Prosecutors said the suspect first told police that a Hispanic man broke into the home, attacked the younger girl and ran off. During questioning, the 14-year-old allegedly confessed to the crime, saying she woke up Tuesday and waited up to 15 minutes before going downstairs, grabbing a knife and attacking the victim.

The girls lived in the same Mundelein home, about 30 miles northwest of Chicago, and attended the same Lake County school, investigators said at a news conference Wednesday.

No adult was home at the time of the slaying. The discovery of the body Tuesday morning prompted a brief lockdown at nearby schools.

"We are very confident this is an isolated incident and there are no other concerns to the neighbors and or the community around it," Guenther said.

Nerheim said he'll decide in several weeks whether to try to have the case moved from juvenile court to an adult court.

The victim and the suspect attended St. John's Lutheran School in Libertyville.

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"We are deeply saddened by the loss of one of our children," school spokesman Steven C. Fuoco told the Daily Herald in Arlington Heights. "We recognize this is a very difficult time for the family, friends and classmates. We have made arrangements for spiritual and professional assistance for our school family."

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