A criminal investigation has been launched after the death of a 3-year-old boy who reportedly ingested fentanyl, according to Apache Junction police.

Police said the toddler swallowed at least one fentanyl pill on Jan. 25 before he was taken to a hospital by his family.

The boy was treated with the overdose medication Narcan before being air-lifted to a second hospital where he died Sunday, police said.

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It’s still unclear where the child came in contact with the fentanyl that was found in his system.

The boy’s name hasn’t been released by police, who said their investigation was ongoing.