EVERETT, Wash. -

A 16-year-old Everett, Wash. boy has been ordered held on $500,000 bail in the death of a woman who was his longtime legal guardian.

The Daily Herald reports bail was set Monday during a brief hearing in juvenile court. The boy was held for investigation of first-degree murder in Friday's death of 37-year-old Gina Latshaw, a woman he called "Mom."

Prosecutors say the seriousness of the allegation requires the case to be handled in adult court.

According to court papers, police suspect the killing was premeditated and say the boy took a number of steps to try to hide his involvement.

The teen called 911 last Friday to report he'd found the apartment door ajar and Latshaw's car outside and was concerned. She was found dead with apparent blunt force head trauma. Police say they found a bloody plastic dumbbell in a garbage can. An apparent match to the dumbbell reportedly was found in the teen's room.