The girl, identified as 17-year-old Angie Morris, was shot in the 9900-block of Linda Lane around 1 a.m.
Morris had texted her new cell phone number to her sister, Kattlin Humphrey, just a few hours before she was killed. Later that night, Humphrey got a devastating call.
"My brother called me on the phone saying she got shot in the head and I needed to go the hospital with my mom," Humphrey said.
Morris was pronounced dead at Lutheran General Hospital. Investigators said the teen was shot in the head at the Heritage Village Pointe Apartments in Des Plaines. Family members said Morris was in a basement apartment with a friend when she was shot.
"We don't know if it was an accident or on purpose but we need answers," Humphrey said. "We just want to know the truth."
Morris was going to be a senior at Glenbrook South High School this upcoming school year, set to graduate early in January. She had dreams of becoming a teacher.
"She was very outgoing. She was dedicated to school. She wanted to be a teacher for special education," said Humphrey.
Sunday night, family and friends gathered outside the Morris' Glenview apartment building for a candlelight vigil in her memory.
No one was in custody Sunday night. The investigation is ongoing, police said.