Among the hundreds of children, lawyers and caseworkers involved in an unprecedented child custody hearing this morning, one person will be noticeably absent the 16-year-old girl whose call for help set in motion the largest child protection case in U.S. history.

Texas authorities say they have not located or identified the girl, though they have said they believe she is among the 416 children from a polygamous(polygyny) sect who were taken into state custody nearly two weeks ago.

Some people are now questioning whether she exists at all.

Though the girl is not key to today’s hearing, her absence looms over the case. Without her, any potential criminal charges that might be brought against members of the sect in the future could be jeopardized, legal experts say.

“This girl is proving to be the linchpin of the entire operation,” Jonathan Turley, a constitutional law professor at George Washington University, told ABC News. “If she doesn’t exist, it’s going to make it very difficult to defend this search. And if you can’t do that, you can’t use anything they found in there.”

In late March, a girl who identified herself as Sarah made several petrified calls to an abuse hot line, complaining that her 49-year-old husband physically and sexually abused her, court records say. The calls prompted government officials to raid the Yearning for Zion Ranch in West Texas and take all the children into custody.

But, several women who live on the Fundamentalist Church of Jesus Christ of Latter Day Saints ranch told ABC News that Sarah does not exist.

“She’s a bogus person,” a woman who identified herself as Joy said earlier this week.

Since the calls, several events have raised questions about Sarah.

Investigators were apparently searching for information about the girl and seized medical records for several women who shared the name given by Sarah during their search of the compound, according to court records. Though an arrest warrant was issued for a man thought to be her husband, police did not arrest him.

On April 4, a day after Texas police raided the compound, an abuse hot line in Arizona received a similar call from a 16-year-old who said she was calling from the FLDS community in Colorado City, Ariz.

The girl said she was being held against her will and physically abused, said Fernando Vender, a spokesman for the Arizona Department of Economic Security, which oversees child protective services.

When Arizona investigators visited a family with the same name provided by the caller, they did not find the girl or any evidence of abuse, he said. Though the case remains open, investigators “could not verify that there was a young girl by that name, with that family and that abuse was going on,” Vender said.

In Texas, state Attorney General Greg Abbott wasn’t so concerned about finding the caller named Sarah.

“It’s irrelevant if the 16-year-old can and will be found,” Abbott told “Good Morning America” today.

He said Child Protective Services “believe they have significant evidence” that abuse occurred and that the children would be in danger if they were returned to the ranch.

Abbott hinted that additional charges could be brought against sect members because women who gave television interviews in recent days “basically admitted to living in a state of bigamy… That also would be a ground for legal prosecution here in the state of Texas.”

But others believe that criminal charges against sect members could be jeopardized if the girl is never identified.

Lisa Wayne, a criminal defense lawyer, said sect members potentially face a variety of criminal charges, including statutory rape, abuse or negligence.

But the sect could challenge the search warrant that police used to enter the compound if the girl is never identified and some of the evidence that investigators found could be suppressed, she said.

“In a criminal case, you have the right to know who may give the government probable cause to come on the premises,” she said.

In her calls to the family shelter, Sarah said she believed she was pregnant with her second child. She claimed her husband was a 49-year-old man named Dale. She said that he raped and beat her, once breaking her ribs, and that she was being held at the ranch against her will.

This weekend, Texas Rangers interviewed Dale Evans Barlow, 50, who is named in the search and arrest warrant used to search the compound, but did not arrest him.

Barlow was briefly jailed in Arizona last year, sentenced to three years’ probation and forced to register as a sex offender after he was convicted of conspiracy to commit sexual conduct with a minor, according to Mohave County, Ariz., Probation Department Chief Friend Walker.

But, Barlow’s lawyer told ABC News that he has not been to Texas since 1977 and Walker said Barlow had been checking in regularly with his Arizona probation officer.

Kathleen Mackert, who said she fled the FLDS community in Colorado City after years of sexual abuse, said she believes Sarah is real but may have been taken out of the compound before police arrived.

“They would want to avoid them getting a hold of her at all costs,” she said.

Mackert said sect members are taught that they should lie to the government and other outsiders. “We were expected to lie,” she said. “They were the enemy.”

Sarah’s absence probably will not affect today’s custody hearing, during which the state will ask to keep the children in state custody and place them in temporary foster homes, legal experts say. More important to the future of the children in state custody will be what the police found once they were inside the compound.

Guy Choate, who is helping to coordinate lawyers for the children, said it’s not unusual for child custody cases to be based on an anonymous call. If caseworkers find evidence of abuse, they are obligated to take action, he said.

Authorities say in court records that there is a widespread practice within the sect of marrying off underage girls to older men. Investigators have found several girls who appear young who are either pregnant or have children, the records say.

More than 350 lawyers are expected to descend on the Tom Green County Courthouse this morning, when a judge will begin to sort out which of the children should be sent to foster homes and which, if any, will be sent back to their parents.

The nearly unprecedented case appears to be the largest child protection case in U.S. history and one that threatens to overwhelm the judges, lawyers and government officials working on it. Each child is entitled to a lawyer, and many of the parents are expected to have lawyers speaking on their behalf as well.

“We’ve never really seen anything like this,” said Lynne Gold-Bilkin, a family law expert.