A Tucson police briefing Thursday on the investigation into the disappearance of Isabel Celis was notable for questions police would not answer.

For example, while they again confirmed previous contact between the Celis family and state Child Protective Services, Sgt. Maria Hawke said police would not discuss the nature of the contact nor say when it occurred.

However, Hawke, a police spokeswoman, did say the previous CPS contact made with the Celis family "was not a TPD-initiated investigation, so it's not something that we have very direct knowledge about."

The Star reported Thursday that state CPS had contact with the family in December. Details of CPS' contact with the family, and how the agency followed up on the report, remain unclear.

In an email, Tasya Peterson, a CPS spokeswoman, said officials would not comment about any case history with the Celis family. She did say the agency is working closely with Tucson police.

Hawke said it would be inappropriate for police to discuss the state CPS case. She referred media to the state agency.

Police have gone before to the residence where the Celis family lives. Hawke said she did not know the nature of the calls. "They're very minimal. When I do a check of the residence, there virtually is no contact there prior to most recently," Hawke said.

She said she could not provide the specific dates when police responded to the Celis home.

Hawke also did not answer questions about anonymous and unconfirmed reports that investigators found a message apparently written by Isabel on her closet wall.

Hawke repeated that the police would not discuss evidence in the case, and that she was unaware of such a discovery.

"The integrity of the investigation is paramount," Hawke said in explaining why police continue to withhold case details.

Hawke started the news conference by stating that while the case has now been labeled an abduction, it could involve a stranger, a family acquaintance or a family member.

The 6-year-old child was reported missing from her midtown home April 21, which led to a massive search by police with up to 250 law-enforcement officers initially working the case.

"Some person is responsible for Isabel's disappearance. Isabel did not just wander off," Police Chief Roberto Villaseñor told the Star on Monday.

The chief also said Isabel's parents, Sergio and Becky Celis, have still not been ruled out as suspects.

"We have eliminated some family members as suspects," said Villaseñor, "and we have eliminated a lot of the sex offenders in the area" of the family's home in the 5600 block of East 12th Street.

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Detectives continue investigating "external" leads that are away from the family, and "internal" leads - family members or persons known to the family, Villaseñor said in his Monday interview with the Star.

A week ago today, Sergio Celis voluntarily separated himself from contact with his wife and their two sons.

This happened after detectives developed information pertaining to the welfare of the boys and shared it with CPS. Villaseñor would not elaborate on the information developed by detectives.

Hawke said Thursday that the father is under no travel restrictions and that he and other family members continue to cooperate in the investigation.

Hawke said police continue to work under the assumption that Isabel is alive, adding that there has been no specific evidence regarding whether or not that is the case.

Today marks Day 28 of the investigation. More than 1,000 leads have been reported.

The 88-CRIME reward for information leading to an arrest in Isabel's disappearance is $50,500.

On StarNet: A collection of the articles, photos and videos related to the search for Isabel is at azstar net.com/isabel

Contact reporter Carmen Duarte at cduarte@azstarnet.com or 573-4104.