An 11-year-old Mundelein girl was stabbed, slashed and cut more than 30 times by her half-sister, who now faces first-degree murder charges, authorities said Wednesday.

The victim was killed Tuesday morning in her home on Woodhaven Court. Her 14-year-old attacker called 911 not long after the murder and waited for police to arrive, Mundelein Police Chief Eric Guenther said.

The older girl attacked her sibling because she felt unappreciated, authorities said.

Police and prosecutors aren't identifying either girl because of their ages.

"(It's) heartbreaking beyond understanding," Mundelein Mayor Steve Lentz told the Daily Herald.

The suspect called 911 about 8:30 a.m. Tuesday, not long after the attack, Guenther said. She indicated a girl had been stabbed, he said.

When officers arrived, the teen let them in, Guenther said. They discovered the victim's body on a bedroom floor.

A small kitchen knife believed to be the murder weapon was recovered in the room, police said. There were signs of a struggle.

The girls were alone when the murder occurred, Guenther said.

An autopsy conducted Wednesday revealed the victim suffered approximately 30 stab wounds to her neck, chest and arms. She also suffered a punctured lung, cuts on her face and defensive wounds on her hands, Lake County Coroner Thomas Rudd said.

The girls' parents were notified of the murder early Tuesday evening, Guenther said. The notification was delayed to ensure police were giving the parents accurate information, he said.

The 14-year-old is in custody at the Lake County juvenile detention center near Vernon Hills. She appeared in juvenile court for a hearing Wednesday.

The suspect was joined in court by her mother, ABC 7 Chicago reported.

She called police Tuesday morning claiming to have been awakened by her sister's screams, and she blamed the crime on an intruder, ABC 7 reported. When confronted with the possibility of DNA testing to identify a hair that was found in the 11-year-old's hand, the teen confessed.

She admitted she stabbed her sister because the younger sibling was "ungrateful" for all she had done for her, ABC 7 reported.

State's Attorney Mike Nerheim said authorities could seek to transfer the case to adult court. Reaching that decision could take a couple of weeks, he said.

Police had been to the house in the past, but not because of anything this serious, Guenther said.

The Lake County Major Crimes Task Force is assisting Mundelein police with the investigation. Chief George Filenko, the group's leader, called the murder "an extremely tragic event that shook even the most seasoned investigator."

The victim attended St. John's Lutheran School in Libertyville, an employee there confirmed. The suspect is enrolled there, too.

A lawyer for the school declined to answer questions but released a statement on behalf of the church and school.

"We are deeply saddened by the loss of one of our children," Steven C. Fuoco said, reading the statement. "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."

Mundelein High School and Fremont Township board member Tami Forman knows the girls and was shocked by the crime.

"I'm dumbfounded," she said. "They were both such wonderful children."

Three schools near the murder scene -- Mundelein High, Sandburg Middle and Mechanics Grove Elementary -- were locked down Tuesday morning as a precaution after the victim's body was found, Guenther said.

The lockdown was lifted after about 15 minutes, once it was clear students were not in danger, he said.

The murder was the village's first since January 2012.

Because of the nature of the crime, Guenther has invited police department employees to talk about it in a private, group setting.

"We will do that in the coming days," he said. "Any case involving tragedy, particularly with a child or young adolescent, is just exceptionally difficult to deal with."