Officers were called around 2:30 p.m. Monday to the Quail Creek apartment complex at 7835 Grow Lane in northwest Houston.
Police say family members came to the apartment earlier Monday to check on a 5-year-old girl, who hadn't been seen for some time.
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When the visitors asked about a foul smell inside the apartment, the mother confessed the source of the odor was the girl's body, according to police.
Officers said she claimed the child had died from ingesting chemicals on Aug. 27. The girl's body had been kept in the closet ever since.
Firefighters who found the girl's body covered it from view, describing it as being in a state of decay, according to police.
"It's very troubling," said HPD Lt. Larry Crowson. "No matter how the child died, you know, whether it's an accidental or intentional death, for a body to be in a closet for several days, that's just unthinkable."
Investigators are now trying to see whether the child's death is consistent with the mother's statement to the police.
An autopsy will determine whether her death was accidental or intentional, and is expected to shed light on what chemical she may have ingested.
Police are also looking into who lives inside the apartment. Investigators said Monday evening that it appeared a man may be living in the unit, and are hoping to speak with him as a potential witness.