According to a criminal complaint, police were called to their apartment on Oct. 3 on a report of an unresponsive baby. Harper told police the child likely swallowed an aspirin while they were lying on the bed.

Harper told officers Murphy had taken Tylenol for a headache earlier and must have forgotten to put the bottle away, the complaint states. Both Harper and Murphy said they saw a tablet inside the child's mouth, and Murphy tried removing it.

Authorities investigating overdose involving 1-year-old in St. Louis Park

The attorney's office said the child was unresponsive and struggling to breathe when paramedics arrived. He was taken to a hospital where doctors had to intubate him due to difficulty breathing inconsistent with Tylenol ingestion.

Doctors then asked the couple what the child had actually consumed so they could better treat it, but they maintained it was aspirin. The complaint said toxicology testing showed it was actually fentanyl.

A search warrant of the couple's home found fentanyl pills in a pair of men's shoes in a closet, the attorney's office said. Harper and Murphy took urinalysis after the baby was admitted to the hospital; Murphy tested positive for fentanyl, while Harper's sample couldn't be analyzed because it had been tampered with, the complaint says.