Updated

Police announced Saturday that, after an investigation lasting more than two decades, they had arrested the killer of a child who was nicknamed Baby Hope by detectives after her body was discovered inside a picnic cooler beside a Manhattan highway in 1991.

During an interrogation early Saturday, the 4-year-old girl's cousin, Conrado Juarez, had admitted sexually assaulting and smothering her, Police Commissioner Raymond Kelly said.

The child's name and the circumstances of her death had been a mystery for two decades. But earlier this week, police announced that a new tip and a DNA test had allowed them to finally identify the baby's mother, a dramatic turnaround in one of the city's more notorious cold cases.

Now they are also revealing the slain girl's name: Anjelica Castillo.

It wasn't clear whether Juarez, 52, had a lawyer. Police said he lived in the Bronx, but that the family had been living in Queens at the time of the killing. They also said Juarez claimed that a relative helped him dispose of the child's body.

Anjelica's naked, malnourished corpse was discovered on July 23, 1991, beside the Henry Hudson Parkway. Detectives thought she might have been suffocated but had few other clues as to what happened.

The case became an obsession for some investigators. Hundreds of people attended a funeral for the unknown girl in 1993. Her body was exhumed for DNA testing in 2007, and then again in 2011.

In July, detectives tried another round of publicity on the 22nd anniversary of the discovery. They canvassed the neighborhood where her body was found, hung fliers, circulated sketches of the girl and a photograph of the cooler and announced a $12,000 reward for information leading to an arrest.

Former detective Jerry Giorgio, who had the case from 1991 until his retirement over the summer, said he remained confident the case could be solved. Assistant Chief Joseph Reznick, who also worked the case, said they never gave up.

"I think reflecting back on what we named this little girl, Baby Hope, I think it's the most accurate name we could have come up with," Reznick said.

Giorgio left the NYPD and went to the Manhattan district attorney's cold case squad, from which he retired this year. "I missed the tipster call by a couple of weeks, damn it," he said.

The tipster led police to Anjelica's sister, who told detectives her sister had been killed. Police matched DNA from Anjelica to their mother. The mother, who was not identified, didn't have custody of Anjelica at the time of the girl's death -- she had been living with an aunt on the father's side, Bavlina Juarez-Ramirez, police said.

Police closed in on Juarez and waited for him Friday outside a Manhattan restaurant where he worked as a dishwasher. He told them he killed the girl at the apartment of his sister -- Juarez-Ramirez. Then, the sister, who is now dead, helped dispose of the body. Kelly said they took a livery cab from Queens to Manhattan where they dumped the cooler.

The cooler, which contained the girl's remains and unopened cans of Coke, was later discovered by construction workers.

Kelly called the arrest a superb case of detective work, and he was proud of his officers. Juarez was being held on murder charges and was awaiting arraignment.

"For me, it makes you proud to be a member of this organization -- they were unrelenting."

The detectives assigned to the case were instrumental in organizing a burial in a Bronx cemetery for the girl in 1993. Hundreds attended the funeral; Reznick gave the eulogy. The girl was dressed in a white frock and buried in a white coffin.

The detectives paid for the girl's headstone that reads: "Because we care."

On the tomb sit two little angels.