Police have found the remains of a six-year-old girl who went missing from her bedroom in Tucson nearly five years ago.

Tucson Police Chief Chris Magnus said Friday that police found the remains of Isabel Celis in a rural area of Pima County about a month ago "not by happenstance."

The remains were identified through an independent, out-of-state lab, Magnus said.

"Obviously this is not the ending that any of us had hoped for, but this is also not the ending of the case. We are working this case very aggressively as we would with any case involving the death of a child," he said.

Celis was last seen April 20, 2012, when she was six years old. Her father reported her missing the next morning after finding she was not in her bedroom.

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Police never named any suspects, but they said they found "suspicious circumstances around a possible entry point" in the home.

Police and volunteers conducted exhaustive searches and even renewed a door-to-door effort to find the girl 18 months after her disappearance.

Tucson Medical Center, where Celis' mother is a nurse, issued a statement on behalf of the girl's family.

"We want to thank the community for the support they have continued to show for Isa over the years and for refusing to give up hope. Now is our time to mourn. We ask for our privacy during this time so that we can do that," the statement reads.

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Medical center CEO Judy Rich said in a statement: "This is not the news we had hoped to hear. Becky has been a member of the TMC family for many years, and our hearts grieve for Isa and her family."

Magnus released few details about the recovery of the girl's remains, saying an investigation is ongoing. He wouldn't say how long the remains may have been in the desert or what caused Celis' death.

Magnus also didn't reveal whether there are any suspects in the girl's death, and he declined to answer questions about how police were led to her body, only saying that it was not a happenstance.

Magnus said the department is still asking for tips and that he believes people might know something about happened to Celis. "We appreciate the fact that this case has been very traumatic. In fact, reverberations of this have gone well beyond Tucson and even Arizona, (and) have affected people throughout the country," he said.