NEW YORK (AP) — The owners of a New York City day care centre where a toddler died and three others were sickened by opioid exposure last week were hiding bags of fentanyl beneath a trap door in the children’s play area, police said.

New York City detectives were executing a search warrant on the Bronx apartment Thursday when they found the narcotics, including a large quantity of fentanyl, and other paraphernalia concealed by plywood and tile flooring. Photos shared by police show bags full of powder inside the “trap floor,” a few steps away from a shelf of children’s toys.

The grim discovery came nearly a week after four young children attending the day care in the Bronx apartment were treated for opioid poisoning. One of the victims, one-year-old Nicholas Dominici, is believed to have died from the exposure.

The day care centre operator, Grei Mendez, and a tenant of the building, Carlisto Acevedo Brito, were charged with murder of “depraved indifference” in Dominici’s death. Authorities are still seeking a third individual, Mendez’s husband and a cousin to Brito.

Prior to finding drugs beneath the trap door, police had already announced the discovery of a kilogram of fentanyl that was stored near mats that children used for sleeping, along with multiple devices used by traffickers for mixing drugs and pressing it into bricks.

Federal prosecutors said Mendez, 36, took steps to cover up the drug operation on Friday afternoon, shortly after realising that some of the children in her care were not waking up from their naps.

Before alerting first responders, she called her husband, authorities said. He was seen on surveillance footage entering the building moments later, then leaving through a back alley with multiple shopping bags.

“All of that happened while the children, the babies, were suffering from effects of fentanyl poisoning and in desperate need of help,” Manhattan US Attorney Damien Williams said at a press conference Wednesday.

During a federal court appearance in Manhattan, an attorney for Mendez said she had no knowledge of the drug operation, while suggesting that her husband was responsible for the drugs.

Brito, 41, did not speak during his court appearance. Inquiries to his attorney were not returned.

Both face up to life in prison if convicted on federal charges of possession with intent to distribute narcotics resulting in death and one count of conspiracy. They were also charged in state court with murder, manslaughter, and assault.