"It's a science," said Ernie Allen, president and CEO of the National Center for Missing and Exploited Children.
"They've searched kind of the obvious places nearby," he said. "The approach in cases like this would be to expand the radius."
Hickory. N.C., police, aided by teams from area sheriff's offices and NCMEC's Adam Team, which deploys specialized search units, have already combed through the family's home, the wooded areas nearby and the property where the 10-year-old's father worked.
Today, Hickory police removed three pieces of bedroom furniture -- including a bed frame, mattress and box springs -- from the house where Zahra Baker lived with her parents, according to the Hickory Record newspaper. Police also carried out two bags of evidence.
Neither area police nor sheriff's offices returned calls seeking comment today.
Allen said those searches and the expanded efforts are all based on a profile of the family and Zahra herself -- where they went, who they talked to, what they liked to do.
And in a case like Zahra's, where police aren't sure exactly when she may have been killed, finding "where was the child last seen alive" can pose difficulties.
"Basically, what you're doing is ruling things out," he said.
And "you always hope you are wrong," said Allen. "You hope you don't find a body."
The search for Zahra, who had lost her hearing and left leg to cancer, was reclassified Tuesday as a homicide investigation.
Zahra's stepmother, Elisa Baker, was jailed on a felony obstruction of justice charge the same day. Baker was already in custody, having been arrested over the weekend on several charges unrelated to her stepdaughter's disappearance.
Though police said she admitted Tuesday to writing a ransom note after demanding $1 million, she has since denied she had anything to do with Zahra's disappearance.
In many of the high-profile missing children's cases, such as Chelsea King's or Elizabeth Smart's, the family becomes an ally to authorities.
That's not necessarily the case in Zahra Baker's.
Though Hickory police have told local media that Zahra's father, Adam Baker, had cooperated he still remains an unofficial suspect for some, along with his wife.
But, Allen noted, "you always look at those closest to the child first."
Since news of Zahra's case went public, neighbors and one relative have come forward to say Elisa Baker had abused the little girl, prompting cries in the North Carolina community for better protection and reporting of suspected abuse.
"I think there was more behind closed doors than what anybody knew," neighbor Kayla Rotenberry told ABC News. "There was once an incident where Zahra's stepmother was whooping Zahra, and she broke her hand on her prosthetic leg. She said when she was whooping her, she hit that youngin's leg and broke her hand."
The Hickory Record newspaper reported that police there have gotten more than 100 leads from the public and are relying on those tips as well as systematic searches of properties frequented by those who were close to the little girl.
Dogs have been deployed not only in Catawba County, where Hickory is located, but also in nearby Caldwell and Burke counties, the Record reported today.
Police have also combed through woods, fields and poured through the family's computers and phone records.
Dogs have found the "presence of human remains" in both of the Bakers' cars, police have said, and "possible blood" was found in one.
ABC News' Yunji de Nies contributed to this story.