The girl was shot to death early Sunday morning as she slept on a couch in her grandmother's home in the 7400 block of South Sangamon in Englewood. McCarthy announced Monday morning that police are questioning a person of interest in the fatal shooting.
"We have a person in custody at this point who is being questioned, let's put it that way, regarding this. We have a lot of information that we have to follow up on before we could get that person charged," he said.
McCarthy would not release any information about the person in custody.
Two teens -- a girl and boy, each 17 years old -- were also injured when someone fired shots through the window of the brick bungalow at about 6:15 Sunday morning.
"If somebody thinks that it is acceptable to fire bullets through the window of a house when you have children sleeping in the house, and people are not willing to come forward to address that, we've got a much bigger problem than perhaps anything the police can solve," said McCarthy.
"Arianna, she was sweet. She loved to play. She loved to come to visit me," said Christine Collins, grandmother, as tears streamed down her face.
Relatives say that Ariana was anxious to spend the weekend with her grandmother so that she could attend a block party in the neighborhood. Monday would have been the first day of school for the first grader at Libby Elementary School.
It is a loss for our school. It is a loss to this community. Anytime you lose a life that young, it just bumps out the promise of positive things that will come out of a community like this," Roshonda Booker, teacher, said.
On Monday, residents created a memorial for the young child.
"She plays with my grandson, you know. Like I say, the kids play together. The teenagers play together. The parents work together and try to keep it safe for the children and watch each other's children," said Englewood resident Tracie.
"Crime is everywhere but for the most part this has been one of the better blocks in the neighborhood," said Marica Hawthorne.
"We do not have a motive yet but we will let you know what it is and how it happened," said Supt. McCarthy.
Neighbors say they are glad that police have someone in custody. There is speculation that the 17-year-old boy shot in the attack was the alleged target of the gunman. He had attended a block party that evening and just crashed for the evening in the home of the 17-year-old female friend. Police would not confirm whether the boy was a target.