A package containing several thousand dollars worth of fentanyl was discovered inside the New York City day care center where a 1-year-old child died from a toxic opioid exposure last week, police and city officials said.

The owner of the day care center, however, maintained she had no knowledge of the presence of the highly potent drug, which sickened three other young children, including an 8-month-old girl who tested positive for fentanyl.

Residue of the drug was found underneath a mat where the children had napped, Joseph Kenny, the New York Police Department’s chief of detectives, said at a news conference Monday evening.

Grei Mendez, who operated the Divino Niño day care inside a Bronx apartment, pleaded not guilty on Sunday to murder charges in the death of Nicholas Dominici. A man who rented a room inside the apartment, Carlisto Acevedo Brito, 41, is awaiting arraignment on the same set of charges.

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Police said they recovered about one kilogram of fentanyl, along with a press device used to combine the drug with other narcotics, inside the closet of a hallway connected to the apartment. A second press was found inside the adjoining room occupied by Brito, according to a criminal complaint.

"We’re not going to allow this incident to take place and ignore this as just another day, another tragedy in the city," New York City Mayor Eric Adams said at the news conference.

He vented frustration at adults who would bring fentanyl into any place with children, noting that even ingesting a tiny amount of pure fentanyl could kill an adult.

"This is just total madness," he said.

An attorney for Mendez, Andres Aranda, said his client lived above the day care center and rented out a room to Brito, her husband’s cousin, for $200 per month.

New York allows home-based day care centers for small numbers of children, as long as they are licensed and inspected.

"Apparently when the day care was not open, people came in and out of the apartment," Aranda said.

Friday was a "normal day" inside the day care center, with Mendez bringing the children upstairs, reading and cooking for them, then putting them to sleep, he said. But when Dominici didn't wake up from his nap, she became terrified, calling 911 and shouting for neighbors, her lawyer said.

Mendez, 36, who also works as a home health aide, was sent to Rikers Island without bail following an arraignment Sunday night. A message left with Brito's attorney wasn't immediately returned.

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The day care facility opened in January of this year. It passed both of its inspections, authorities said, including a surprise visit made by inspectors on Sept. 6.

When emergency personnel arrived at the apartment Friday afternoon, they discovered Dominici, as well an 8-month-old girl and a 2-year-old boy, showing signs of opioid intoxication. Medics administered Narcan, an overdose-reversing drug, to all three, helping to counter the symptoms of the 8-month-old and 2-year-old.

Dominici was pronounced dead at a hospital in the Bronx later that day.

A fourth child who had attended the day care was taken to a hospital by her mother after showing signs of opioid exposure, including shortness of breath and unresponsiveness.

It remains unclear how the children may have been exposed to the drugs. Dominici’s cause and manner of death are pending further study, according to the city’s medical examiner’s office.

Fentanyl, a synthetic opioid that is up to 50 times stronger than heroin, has become a primary driver of soaring overdose deaths both nationally and in New York City. Illegally made fentanyl is often added to other drugs, including heroin, cocaine and methamphetamine, to increase its potency.

Unintentional drug overdoses among children are also on the rise, with opioids the most common substance contributing to fatal poisoning of kids.

In the overwhelming majority of cases, children were found to have orally ingested the substance, rather than touching or inhaling it in the air, according to a 2019 study published in the Journal of Pediatrics.