(KRON) — A 23-month-old boy died in October after he was exposed to fentanyl, the Fremont Police Department said. The boy’s mother was arrested on Tuesday.

On Oct. 18 at about 8:30 a.m., the victim arrived at a local emergency room unresponsive and not breathing, police said. The child was driven to the hospital by his mother and other family members. The boy was later pronounced dead.

FPD began investigating the death and determined that the boy was initially found unresponsive in the bedroom he shared with his mother on the 4300 block of Gina Street in Fremont.

Police served a search warrant at the home and found “items associated with illicit drug use” inside the bedroom. Those items were tested and the presence of fentanyl was confirmed. The mother, 26-year-old Fremont resident Sophia Gastelum-Vera, had electronics in the room where she talked about fentanyl use and possession, FPD said.

A toxicology report revealed the baby had “a high level of fentanyl” in his system when he died, per police.

Gastelum-Vera was booked into the Santa Rita Jail and charged with involuntary manslaughter, willful cruelty to a child, possession of a controlled substance, and possession of injection/ingestion device/controlled substance paraphernalia. FPD detectives are still investigating the death.