Hickory, North Carolina (CNN) -- Investigators spent a second day searching a lot where the father of a missing 10-year-old girl worked after declaring the girl's disappearance a possible homicide Monday.
Hickory Police Chief Tom Adkins said investigators have been unable to find anyone outside Zahra Clare Baker's immediate family who has seen her in the last month. The girl's stepmother, Elisa Baker, has been charged with obstruction of justice after admitting to writing a ransom note found at the family's home, and the investigation has shifted from a possible abduction into a homicide probe, Adkins told reporters Tuesday.
"We cannot confirm with any confidence how long Zahra has been missing," he said.
Monday evening's search was the second time investigators have been out to the lot north of Hickory where the girl's father, Adam Baker, worked, said Nancy Webb, who lives next door to the site. Baker would help his employer bring piles of wood and brush to the lot, where it was dumped into a wood chipper and turned into mulch, Webb said.
"They've got a lot of lights out back of the house. It looks like they are doing a search around a brush pile, and that's all that I can see from the house here," Webb told HLN's "Nancy Grace."
Zahra's stepmother, Elisa Baker, admitted to writing the ransom note Monday night dudring an interview at the jail where she was being held on an unrelated bad-check charge, Adkins told reporters. She then requested a lawyer, he said.
Zahra was reported missing about 2 p.m. Saturday. Police have said her father and stepmother reported she was last seen sleeping in her bed about 12 hours earlier, at 2:30 a.m.
A search warrant application filed in the case said the case began with a call about a burning mulch pile at the home about 5:30 a.m. Saturday. Firefighters found a Chevrolet Tahoe with its passenger door open and a power company envelope with handwriting on it on the front windshield, the search warrant said.
Firefighters notified police, who approached the SUV and smelled the odor of gasoline coming from inside. The note written on the envelope was addressed to a "Mr. Coffey," identified in the search warrant as Adam Baker's boss, Mark David Coffey.
"Mr. Coffey, you like being in control now who is in control," the note said, according to the search warrant. "We have your daughter and your pot smoking red head son is next unless you do what is asked 1,000,000 unmarked will be in touch soon." In the bottom right, the note said, "no cops," according to the warrant.
Coffee and his only daughter were at the residence at the time of the fire, the warrant said. CNN affiliate News 14 Carolina reported Coffey owns the home.
Adam Baker called police about 2 p.m., saying someone had poured gas in his car and left a note saying they had his boss' daughter, according to the search warrant. Baker told police he believed the person who left the note had kidnapped Zahra.
The Bakers consented to a search of their home, the warrant said. A cadaver dog indicated the possible presence of human remains in or on the Chevrolet Tahoe as well as a burgundy Toyota Camry on the property, it said. Authorities were testing swabs taken from the Tahoe to determine if blood was also present, according to the warrant.
The girl -- a bone cancer survivor, according to CNN affiliate WCNC -- uses a prosthetic leg and hearing aids. The hearing aids have been found, but not the prosthesis, Adkins said.
Elisa Baker was arrested Sunday morning on four counts of writing worthless checks, said Eric Farr, a spokesman for the Catawba County District Attorney's office. Farr said she faces other charges in different counties, including a felony larceny count and other bad-check charges. She is being held on $31,500 bail.
Her court-appointed attorney on the felony charge, Jared Amos of Morganton, North Carolina, said Tuesday he could not comment on the case, as his representation is limited to that charge.
Adkins said Adam Baker faces similar charges, but police have held off serving an arrest warrant while he cooperates with investigators. And police said in a statement they are are "working several leads, specifically addressing Zahra's life before she disappeared."
Kayla Rottenberry, a former neighbor, said child welfare officials visited the Baker home twice. Elisa Baker told Rottenberry that someone "called and complained about black eyes and her keeping [Zahra] locked in her room," Rottenberry said.
"Her eyes had blue underneath -- not all around [her] eyes -- but her stepmom said her eyes got like that because she was sick," Rottenberry said. She said she saw Baker yelling at her stepdaughter as well, but didn't report the behavior "because they were already on her."
"Whenever she wouldn't walk right, she would holler at her," Rottenberry said. "She would fuss at her when she wasn't walking right and would ground her."
And Brittany Bentley, who is married to Elisa Baker's nephew, told HLN that the girl "wasn't in very good living conditions, not at all for a 10-year-old."
"I remember Elisa coming out of the bedroom one day, saying her hands hurt from spanking Zahra so much," she said. "I know she spanked way too hard, what I consider beating. I know about letting her out five minutes, just to eat, and that was it."
North Carolina's social services system is state-supervised but county-administered, meaning reports are handled in the county where they are made, said Lori Walston, spokeswoman for the state Department of Health and Human Services. However, she said workers are bound by strict confidentiality laws and would not be able to comment on the case.
Adkins asked for anyone who has seen Zahra in the last month to come forward. Investigators have learned that an inspection may have been scheduled at the home, and are interested in speaking with the inspector, he said.
An emotional Adam Baker told ABC's "Good Morning America" on Tuesday he can't be sure his wife is not involved in Zahra's disappearance.
"Until they've completed their investigation and can tell me some more, I can't honestly say," he said.
HLN's Natisha Lance and CNN's Ashley Hayes contributed to this report.