Read more about the case from CNN affiliate WCNC.
Morganton, North Carolina (CNN) -- Investigators spent another fruitless day Thursday looking for a 10-year-old North Carolina girl missing since last weekend and now believed dead, the local sheriff said.
Authorities spent a third day combing an area about 20 miles north of Zahra Clare Baker's home in Hickory, North Carolina. This time, as many as 70 searchers were backed by dogs and a backhoe that was used to clear piles of wood and mulch, Burke County Sheriff John McDevitt said.
The goal of Thursday's effort was to eliminate the possibility that Zahra's body had been dumped on the roughly 60 acres, McDevitt said.
"For the community's sake, we wanted to clear this area," he said. "And for a large majority, we did that."
Zahra was reported missing Saturday afternoon. Her disappearance is being investigated as a homicide, and her stepmother has been arrested on charges of obstructing justice.
The searches near Morganton started Tuesday as investigators focused on a lot where Zahra's father, Adam Baker, frequently worked hauling loads of wood and brush to be mulched. Wednesday, investigators came up empty after draining a pond next door.
Police said this week that the stepmother, Elisa Baker, admitted to writing a fake ransom note that was left at the family's home. She was arrested Sunday on an unrelated charge of passing bad checks, prosecutors said.
Elisa Baker remained jailed on those charges Thursday. Her bail has been set at a combined $70,000, an amount her lawyer called "excessive." Police said Adam Baker also faces bad-check charges, but is not being arrested while he assists police.
"At this point, he's doing what we ask him to do. If we need him to do something, he shows up," said Clyde Deal, Hickory's deputy police chief. Deal said other searches have been conducted, but the warrants have been sealed and no details are being released.
Police said earlier this week that no one outside the girl's immediate family had reported seeing her for nearly a month. But Deal said Thursday that another witness had come forward to say they had seen Zahra in mid- to late September.
Zahra reportedly suffered from bone cancer and used a prosthetic leg and hearing aids. The hearing aids have been found, but not the prosthesis, Hickory Police Chief Tom Adkins has said.
Relatives and friends of the family have alleged that Elisa Baker physically abused Zahra and said she was reported to state social services officials. The North Carolina Department of Health and Human Services has declined comment on the case.
Hickory is about 60 miles northwest of Charlotte.
HLN's Natisha Lance and Beth Carey contributed to this report.