Tucson police labeled the case of Isabel Mercedes Celis as suspicious and a "possible abduction" and were chasing down leads and canvassing the neighborhood all weekend.
Isabel's parents told police they put the youngster to bed Friday night, but she was gone when they checked on her Saturday morning, KVOA-TV, Tucson, said.
Detectives had yet to determine if someone broke into the home, the report said.
Police fanned out around the neighborhood Saturday and served a number of unspecified warrants, KVOA said. They were assisted by sheriff's deputies, the FBI and the U.S. Marshals Service as well as tracking dogs from the state Department of Corrections.
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