Zahra Baker, 10, waits to get a hearing aid at...

Zahra Baker, 10, waits to get a hearing aid at an event Charlotte Motor Speedway in May 2010. The girl was reported missing on Oct. 9, 2010. Credit: AP

Police indicated Tuesday they believe someone killed a 10-year-old North Carolina girl whose bone cancer left her with a prosthetic leg and hearing aids, saying they were shifting from a missing person search to a homicide investigation.

Zahra Clare Baker was reported missing Saturday, but police said they can’t find anyone outside the household who has seen the girl alive in a month. Relatives described the child’s life as miserable, saying she was locked in her room for most of the day and was punished over little things.

Hickory Police Chief Tom Adkins said at a news conference that the girl’s stepmother confessed to writing a ransom note found at the house where the girl lived, and she has been charged with felony obstruction of justice in the case. Elisa Baker, who was being held on unrelated charges, has also asked for an attorney.

Uncertainty over when the girl was last alive has stymied efforts to search for the girl, the chief said.

"We understand the public wants to help find Zahra. The problem is we cannot confirm with any confidence how long Zahra has been missing," he said at the news conference. "Without this information, we cannot positively select the area to search for her."

Adkins did not take any questions and did not offer further explanation of why the case was being treated as a homicide. A search warrant revealed on Monday that police dogs detected the smell of human remains on cars belonging to the father and stepmother.

The girl’s father, Adam Baker, has not been charged in the case, though the chief said previously he hasn't been ruled as a suspect. Police say he’s cooperating in the case.

Adam Baker has said it was possible his wife could be involved in the disappearance, and other relatives echoed those remarks.

"I just think this was something for a long time that we knew was going to happen, everybody that was close to the family," relative Brittany Bentley said on CBS' "Early Show" on Tuesday.

Bentley, who is married to Elisa Baker’s nephew, said she would have Zahra over for weekends and the girl would get mad when it was time to return home.

Zahra "was locked in her room, allowed five minutes out a day to eat, that was it," Bentley said. "She was beat almost every time I was over there for just the smallest things. Elisa would get mad, she would take it out on Zahra, things the kid didn't deserve. She just had a horrible home life." Neighbors also feared the worst.

"There were warning signs along the way, but you never want to think the worst,” said former neighbor Kayla Rotenberry.

Zahra was reported missing Saturday afternoon after a yard fire at the home. The stepmother said she last saw Zahra sleeping in her room about 12 hours earlier, though Adkins has indicated he doesn’t believe the timeline the couple gave him.

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