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When Sian Jung heard a boom in her north suburban apartment building Saturday morning, she thought it was fireworks, something she’s used to because kids in the complex set them off frequently, the 15-year-old recalled Monday.

She didn’t know it was a gunshot until news spread that her neighbor, and classmate, had died.

The Cook County sheriff’s office on Monday continued to investigate the fatal shooting of 16-year-old Lilly Bova over the weekend in unincorporated Northbrook. Meanwhile, Bova’s life — and loss — loomed over her north suburban community, as students at Glenbrook South High School, where Bova was a sophomore, returned to class for the first time after spring break and neighbors took in the shock of the shooting, something they said so rarely happened in their area.

Around 11 a.m. Saturday, officers responded to a call of a potential gunshot victim at Salem Walk Apartments in the 3600 block of South Salem Walk, according to a report from the sheriff’s office. When officers arrived, they found a 16-year-old girl, later identified as Bova, shot inside an apartment, according to the sheriff’s office and the Cook County medical examiner’s office.

Jung, who lives in Salem Walk Apartments, was hanging out outside in the complex at the time, she told the Tribune. Also a sophomore at Glenbrook South, Jung said she wasn’t very close with Bova but that they were friends of friends.

“It’s shocking that it was near us,” she said. “It’s scary.”

Bova was transported to Advocate Lutheran General Hospital in Park Ridge, where she was pronounced dead, authorities said.

Salem Walk residents were in shock Monday. Helena Naiden said she saw Bova’s body being taken from the apartment in an ambulance at around 11:10 a.m., she said.

Naiden spoke fondly of Bova, telling a story of her young neighbor running out of her apartment in her white socks to help her pick up spilled trash just “a few months ago.”

Fellow neighbor Bobbie Montgomery said she didn’t know Bova but was surprised to learn about the shooting.

“I was standing (in the kitchen) washing dishes and then all of a sudden all these sheriff’s cars started pulling into the parking lot,” she remembered. “(There wasn’t) like a big fight or big commotion, or like a whole bunch of shots or anything. I didn’t hear anything.”

Jeanie Gamorot, who lived in the complex on the first floor near Bova and her family, said, “We’re very quiet here.” She described the Bova family as “very nice.”

“They always say hi,” she said. “They always smile. … It’s just very sad.”

As of Monday, the medical examiner’s office still listed Bova’s cause of death as pending, while detectives searched for a person of interest.

Following news of Bova’s death, Glenbrook South High School Principal Barbara Georges, in a message to students and families Sunday afternoon, said Bova’s “kind-hearted and optimistic nature will be sorely missed.”

“Though Lilly was a quiet spirit, her teachers and those who knew her best said she loved deeply and was positive and mature beyond her years,” Georges continued. She said the school’s people were keeping Bova’s family in their thoughts as they grieve “this unimaginable loss.”

Bova’s father, Anthony Bova, did not immediately return a request for comment, but took to social media Sunday to share a message with friends and family.

“You are God’s girl … don’t ever forget that. You are not random, forgotten or overlooked. Heaven knows your name,” his post read. “Walk with confidence. Walk with grace. Walk like the daughter of a King, because that is exactly who you are.”

At Glenbrook South, senior Amy Tuvshintur said her teachers talked about Bova in almost every one of her classes.

“Most of the students have been sharing memories they had with her,” said the 18-year-old, who didn’t know Bova firsthand. Tuvshintur said teachers also stressed that students can make use of support that’s available on campus. Counselors and social workers via the Glenbrook School Health Center were available to students throughout the day Monday.

Georges, in her message over the weekend, said that as authorities continue their investigation, “we are holding our entire community close and will navigate this difficult time together.”

Although Glenbrook South senior Francesca Canzaniello didn’t know Bova personally, Georges’ email stuck with her.

“When I first read the email, I was thinking about it a lot,” the 17-year-old said. “A 16-year-old died with a whole life ahead of them. It’s sad to think about.”

As of Monday night, a GoFundMe page established in support of Bova’s father had garnered nearly $4,900. Funds raised will go toward helping Bova’s father give his daughter “a service, a burial, a celebration, whatever he needs to do for her,” according to the page, which was launched by Vicki Clark, who identified herself as a family friend of the Bovas.

“Nobody plans on having to do this for a teenager,” the fundraiser read.

The GoFundMe lists April 9 as the date of Bova’s funeral service.

Meanwhile, in a post to social media on Sunday, the Youth Peace & Justice Foundation — also known as the Uvalde Foundation For Kids — said it planned to plant a memorial tree in Bova’s honor in Francis Marion National Forest in South Carolina. The foundation also said it is also offering a reward of up to $5,000 for information on the shooting.

Authorities encouraged anyone with information to contact sheriff’s police detectives at 708-865-4896.

The Tribune’s Madeline King contributed.