Authorities in North Carolina scoured the property of a tree service company on Wednesday, focusing on a wood chipper and mulch pile in their search for the remains of missing 10-year-old Zahra Clare Baker. 

A team of searchers and police dogs spent hours investigating the Burke County, N.C., property where the girl's father, Adam Baker, is employed, the Charlotte Observer reports.

Police charged the girl's stepmother, Elisa Baker, with felony obstruction of justice on Tuesday after she admitted to writing a fake ransom note found on the windshield of one of the family's vehicles. Authorities believe that the note, which was addressed to Adam Baker's boss and which demanded $1 million, was designed to throw investigators off track in their search for Zahra.

Hickory Police Chief Tom Adkins said Elisa Baker confessed under police interrogation to writing the note and requested an attorney. She appeared in court on Wednesday and showed no emotion as the judge told her she could be sentenced to up to 30 months in prison if convicted of felony obstruction of justice. Judge Gregory Hayes said a review of the family's finances show Baker is eligible for a court-appointed attorney and assigned her a lawyer.

Adkins said that Baker's confession prompted authorities to shift their search from a missing person's case to a "homicide investigation."

K-9 units detected the scent of human remains on two vehicles at the Bakers' home in Hickory, N.C., on Monday, a police search warrant revealed. Residents reportedly told the Charlotte Observer that search dogs also picked up on the scent of blood at Real Tree Services in Morganton, N.C., where Adam Baker works as a laborer.

Investigators used backhoes and other equipment late Tuesday to search the company's property, focusing on a 50-foot-wide pile of mulch, according to the newspaper. 

The News Herald in Morganton also reports that investigators are examining an industrial wood chipper belonging to the company's owner, Fred Causby, who reportedly hired Baker about six months ago.

The tree service company is approximately 19 miles from the Bakers' home.  

Adkins told reporters at a news conference Tuesday that he "cannot confirm with any confidence how long Zahra has been missing."

"We can't confirm anyone has seen Zahra within the past month," Adkins said. "Without this information, we cannot positively select the area to search for her." 

Zahra, described by neighbors as an upbeat girl who was battling bone cancer that left her with a prosthetic leg and hearing aids, was reported missing Saturday afternoon -- nearly 12 hours after Elisa Baker said she last saw her sleeping in her room. 

Elisa Baker was already being detained after she was arrested Sunday on a dozen charges unrelated to Zahra's disappearance -- including communicating threats, writing worthless checks, larceny and driving with a revoked license.

Adam Baker said during a morning TV interview on Monday that it was possible his wife could be involved in the disappearance, which was reported after a fire in the home's yard. 

"I hate to say it but I don’t feel good about this," said a family friend who spoke to FoxNews.com on condition of anonymity. "I really think Elisa had something to do with it." 

Elisa Baker told her husband she last saw Zahra sleeping in her bed at 2:30 a.m. Saturday, about 2 1/2 hours before the fire was reported. Adam Baker said he was panicked after the fire, but didn't immediately check on his daughter.

Zahra, who is home-schooled, had two hearing aids, both of which were left at the house. Police said the girl also has a prosthetic leg from the knee down.  

Family friends described the girl as shy but constantly smiling, in spite of her health problems.

To relatives and former neighbors, Elisa Baker had a short fuse. In interviews and court documents, they portrayed her as nasty-tempered and willing to use a gun or her fists to settle an argument and say her disabled stepdaughter usually bore the brunt of her rage.

"She was always beating her," former neighbor Karen Yount said Tuesday. "I told her to stop but she wouldn't listen to anyone. That poor girl."

Kayla Rotenberry, a former neighbor, said she and her fiance were good friends with the Bakers when they lived in the nearby town of Sawmills, and saw Zahra often. About six months ago she noticed that Elisa Baker's hand was swollen, Rotenberry said.

"She told me that she was trying to spank Zahra, but hit her on her prosthetic leg," she said. "When Adam asked her about the injury, she said she fell and hurt her hand. She didn't want him to know. She knew he would be mad."

Another former neighbor, Brandy Stapleton, 22, of Lenoir, said that Elisa Baker told her the same story about how she injured her hand. "She wasn't the person everyone thought she was."

Adam Baker is from Australia, and met his current wife over the Internet, Stapleton said. Zahra's mother lives outside the U.S.

Click here for more on this story from the Charlotte Observer

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The Associated Press contributed to this report