The call came in to 911. The ambulance pulled up to the Harlem apartment building, and a 4-year-old boy’s skeletal frame was loaded into the back.

The mother told the police she did not know how her son came to be in a condition later described by authorities like this: Weight, 19 pounds — about normal for a 1-year-old. Hair growing on his face, a sign of long-term malnutrition. Thinning hair on his head, matted with feces.

By the next morning, Oct. 14, the boy, Jahmeik Modlin, was dead. His three older siblings, ages 5, 6 and 7, also severely malnourished, were hospitalized.

Since then, there has been a steady drumbeat of horrific details from the police and prosecutors about what went on in the family’s filthy sixth-floor apartment.

A stocked refrigerator turned to the wall to keep the children out. Childproof locks on the cupboards where food was kept. A statement from Jahmeik’s mother, Nytavia Ragsdale, 26, that for weeks he had been vomiting and then eating his vomit. A statement from his father, Laron Modlin, 25, that he did not notice his son wasting away because he was busy playing video games or on his phone.

The family had been on the radar of the city’s child welfare agency, the Administration for Children’s Services, on and off since 2019, before Jahmeik was born. But A.C.S. closed its last case with the family in 2022 after determining that the children were not being mistreated, according to a person who saw their social service records.