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Dad asked to stay away from missing Tucson girl's brothers

Child welfare officials have increased their involvement in the case of a missing 6-year-old Tucson, Ariz., girl and have forbidden the father from having contact with his other children, sources tell NBC News.

While Isabel Celis’ parents, Sergio and Rebecca Celis, have been cooperating with authorities since the child disappeared more than three weeks ago, neither parent has been ruled out as a suspect, police say.

“Until we find conclusive evidence that leads down one path, we are not going to close the doors on anything,” Tucson Police Chief Roberto Villasenor told NBC's "TODAY" on Monday.

Police say while involvement from Child Protective Services is common practice involving cases with missing children, “CPS instituted certain measures to ensure the continued welfare of the Celis children,” according to a statement released Friday.

In addition to Isabel, the Celises have two older sons, who are now in the custody of their mother, police say. The mother is no longer living with Sergio Celis, according to local media reports.

Isabel's father was reportedly the last person to see the girl. He reported her missing around 8 a.m. April 21 after her mother had left for work and he went to wake up the child. Isabel was not in her bedroom, he told police, and a room window was opened and its screen removed. Sergio Celis said he last saw Isabel around 11 o'clock the night before, when he put her to sleep.

Criminologist Casey Jordan, who has been following the Tucson investigation, said child welfare officials must have had established grounds for their recent involvement. “I don’t know that investigators are circling back to the family so much as they never left the family,” she told "TODAY."

Volunteers have canvassed the area, posting fliers that include a photo of the girl. Investigators have searched several homes in the neighborhood, dug up and combed the nearby landfill and searched drainage systems in Tucson.

More than 1,000 tips have poured into the police department, which has since reported spending $1 million in the investigation, according to local media reports.

Isabel's parents have made several public, emotional pleas for the safe return of their daughter in the days after her disappearance.

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