The teen was found dead in a home in the 7800-block of West 167th Street, Tinley Park police said.
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An autopsy ruled her death a homicide, saying she died of multiple injuries, the medical examiner's office said.
Police said a person of interest was identified, and there is no threat to the community.
The Cook County Medical Examiner's Office identified the victim as Mia Maro.
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The principal of Andrew High School, where she attended, shared the news with the school's community in a letter Monday, writing in part, "Today is a very sad day for the Andrew High School Community as we grieve the loss of senior student Mia Maro... We extend our condolences to Mia's family and ask that everyone keep Mia in their thoughts and prayers."
Monday night friends and classmates flocked to a growing memorial outside her family's home to pay tribute to Maro.
"She was a few weeks away from graduating, and it's a very happy time, and just to have life cut short like that is just really very, very sad," said Andrew Brescia, neighbor.
Police said the teen was found dead in her home Sunday evening, and neighbors said her father was also pulled from the home on a stretcher as other relatives arrived, distraught. They described a chaotic scene, with much shouting.
"You could see the emotion change from confusion to anger to distraught very, very fast," Brescia said.
Administrators at Andrew High School said counselors will be on hand all week for her classmates.
The home remains cordoned off as police continue to investigate.
Tinley Park police did not respond to ABC7's request for an interview, but in a statement said more information is pending.
The Sun-Times Media Wire contributed to this report