EVERETT, Wash. -- Snohomish County sheriff's detectives have recovered the remains of a girl who died at least four years ago and whose body was hidden in a plastic storage bin.

Detectives seized the storage tote when they served a warrant at a residence in Everett last Saturday. On Sunday, detectives and the medical examiner's office confirmed the container contained the body of a girl. The identification of the remains and the cause of death have not been determined.

The sheriff's office began investigating the girl's disappearance after receiving information from a relative. During their investigation, detectives learned that the girl's relatives believed she had died when she was four years old and was under the supervision of her mother.

The mother and her then-boyfriend (they have since married) had a history with police and "panicked" when they discovered the girl had died, according to the sheriff's office. Relatives believed the two had wrapped the girl and put her body in a storage container, which they kept in their residence until the girl's body began to decompose and smell.

The two allegedly poured concrete over the body in the container, then kept the bin for several years more, eventually stashing it at a relative's residence after they moved from their home.

The girl’s mother told family members, including her other children, several versions of how the girl died. The girl was never reported dead or missing to any law enforcement agency, nor was she ever enrolled in a school. She would have been nine years old.

At this time, no arrests have been made, and the circumstances surrounding the girl’s death and the disposal of her body remain under investigation.

The sheriff's office is also working with Child Protective Services and the Washington State Department of Social and Health Services in the investigation.