Felix Herrera Garcia’s wife called him on a September afternoon last year, just after she had discovered that three children in her Divino Niño day care center would not wake up.

He ran to the basement facility in the Bronx, which prosecutors say he had long used to store and package opioids. Mr. Herrera Garcia, prosecutors said, would have stepped over a 22-month-old boy lying on a kindergarten mat, poisoned by fentanyl.

Mr. Herrera Garcia was gone before an ambulance arrived, beginning a two-week flight to Mexico before he was arrested in California. The 22-month-old, Nicholas Dominici, was dead before Mr. Herrera Garcia had made it out of the Bronx.

On Wednesday, Mr. Herrera Garcia, who pleaded guilty in June to possessing narcotics with the intent to distribute and conspiring to distribute narcotics resulting in serious injury and death, was sentenced in Federal District Court in Manhattan to 45 years in prison.

The events last year at Divino Niño, in which four healthy toddlers were grievously sickened within hours of being dropped off by their parents, horrified people across New York City and beyond.

Additional details in court documents provided the most detailed description yet of the lethal episode and the events surrounding it. The documents include new information about how Divino Niño functioned as a secret stash house, with the kitchen implements used to prepare children’s meals doubling as drug-packaging tools, a circumstance that prosecutors said was probably responsible for the poisonings.