By Paige Tortorelli and Tim McNicholas

CHICAGO (CBS) — A grieving mother reached out to WBBM-TV in Chicago a year after her daughter unexpectedly passed away in North Carolina. Debbie Heater has subpoenaed documents, and called local law enforcement in North Carolina, but still can’t get clear answers about how her daughter’s death is being investigated. WBBM reporter Tim McNicholas looked into her lingering questions.

Shortly after Courtney Heater’s boyfriend made a frantic 911 call, an ambulance rushed to a rural North Carolina home. EMTs pronounced her dead at 4 a.m. on Feb 2, 2020.

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“I just didn’t believe it,” said Debbie Heater, her mother.

Debbie, who lives in Plainfield, was shocked when she heard the news. “How could she be gone? She’s 24 years old. She was an athlete. She was healthy,” she said.

The news devastated Debbie, and Cassidy Mootrey, Courtney’s childhood friend. “She was the friend you could always go to. She was always there for everyone,” Cassidy said.

Even more devastating, nearly a year later, they’re unable to piece together what happened the night Courtney died. “She was incredible. I was very lucky to be her mother,” Debbie said.

Courtney moved to Columbus County, North Carolina in 2018 to live with her boyfriend. But her childhood home is still filled with memories of her. Pictures of rugby, bike riding, and tailgating are a stark contrast to the ones Courtney took during her final months.

A police report points to Courtney being assaulted by her boyfriend. So do hospital emergency room paperwork and text messages. “It’s devastating,” Debbie said.

Six months after Courtney’s death, Debbie finally received the autopsy report. Noted in the report: more abuse, including blunt force trauma to the head, chest, abdomen, pelvis, and extremities. However, the cause of death was ruled to be an accidental heroin and fentanyl overdose.

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Debbie and Cassidy said they’re worried Courtney’s boyfriend might have forced her to take the drugs. “Just because someone has drugs in their system does not mean that they took it,” Cassidy said.

But the lead detective on Courtney’s case seems to disagree. “Based on the autopsy there is no further investigation for a homicide,” said Columbus County Sheriff’s Chief of Detectives Paul Rockenbach.

To help her keep track of Courtney’s case, Debbie recorded her calls with the Columbus County Sheriff’s Office. “I’m not gonna sit here and say something didn’t happen,” Rockenbach said. “I would have the same questions you do.”

Debbie said the answers she’s received are inconsistent. So are the answers CBS 2 received. Rockenbach said the department offered to cover the cost of Debbie’s flight to North Carolina, but she said that’s not true. He also told us all nearby neighbors were interviewed.

McNicholas reached out to a neighbor who lives just 243 feet away. She said she’s never been contacted. “It’s like [Courtney] wasn’t worth anything,” Debbie said.

“This has been a year, almost. It’ll be a year, in February, of non-stop research,” adds Cassidy.

Unable to get clear answers about where the investigation stands, Debbie filed a subpoena for the sheriff’s department’s case file, but all she could obtain was the 911 call, a two-page police report, and an EMT report that’s missing the third page. “Every day I think I’m going to know today, something’s going to come in the mail, or I’m going to get an email or phone call. We’re going to know today. And at the end of the day, it doesn’t happen,” Debbie said.

For now, Debbie’s cherishing her memories of Courtney.

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The sheriff’s office said the investigation is still open, but wouldn’t specify if any interviews have been conducted, aside from those in the initial two-page police report.