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The parents of a 15-month-old boy have been charged with the murder of their son, who died of fentanyl poisoning in Jurupa Valley two months ago, officials announced Monday.

The father, 22-year-old Adler Metcalf, was initially only charged with child endangerment but the Riverside County District Attorney’s Office added a murder count Monday at his first court appearance, according to a news release.

Metcalf did not enter a plea Monday and his arraignment is scheduled to continue Tuesday.

The toddler’s mother, 20-year-old Sandy Acuna, has also been charged with murder, the D.A.’s office said. She was not cleared by the jail she’s in to appear in court Monday and will be arraigned at a later date, officials said.

Around 4:20 a.m. Sept. 1, deputies responded to a call of a juvenile who was not breathing in the 5400 block of 34th Street in Jurupa Valley, the Riverside County Sheriff’s Department said.

The deputies immediately gave medical aid, but the child was declared dead.

Following an extensive investigation, it was determined the 15-month-old boy “was a victim of homicide due to a Fentanyl overdose,” the Sheriff’s Department said. It was determined the child’s parents, Metcalf and Acuna, were responsible for possessing the fentanyl that killed their child, officials said.

They were arrested on Nov. 10 and remain in custody on $1 million bail.

Fentanyl is a synthetic opioid that is around 100 times stronger than morphine and 50 times more potent than heroin, according to the U.S. Drug Enforcement Administration. Just 2 milligrams of fentanyl can be lethal — depending on a person’s body size, tolerance and past use. 

Synthetic opioids like fentanyl are the primary driver of overdose deaths in the country, according to the Centers for Disease Control and Prevention. The number of overdose deaths involving synthetic opioids — mainly illicitly manufactured fentanyl —  climbed 55.6% between 2020 and 2021.