The New York Police Department received a tip from someone after a publicity push over the summer, police officials said. The tip led to the woman, whose name was being withheld amid a homicide investigation.
"A DNA match was made with the mother, and the mother is cooperating," Police Commissioner Raymond Kelly told reporters on Tuesday.
Kelly declined to discuss the case further as investigators try to determine the circumstances of the 3- to 5-year-old girl's death.
"Obviously, homicide is a distinct possibility here, so we're going to go forward in that direction," Kelly said.
Besides the mother, police also were speaking to other people. No official suspects have been named.
The case dates to July 23, 1991, when a road worker smelled something rotting and discovered the girl's remains inside a picnic cooler along the Henry Hudson Parkway. Her body was unclothed and malnourished and showed signs of possible sex abuse.
Detectives theorized at the time that she had been suffocated before being dumped like garbage on a grassy incline. They estimated she was dead six to eight days before the cooler was found.
In an interview in July, retired Detective Jerry Giorgio said he had pursued hundreds of leads but none panned out. He had the case from 1991 until he retired from the force. Later, as an investigator for the Manhattan district attorney's office, he kept up with it. His name and contact information are still on a website dedicated to the girl.
"It was so frustrating," he said recently. "We initially thought we'll get her identified and go from there and probably solve the case. It didn't happen."
As the frustration mounted, so did detectives' affection for the victim. They began calling her "our baby." Eventually she became "Baby Hope," because they hoped and prayed they'd solve the case, Giorgio said.
Giorgio was instrumental in organizing a 1993 funeral for the girl that was attended by hundreds. The girl was dressed in a white frock and buried in a white coffin.
Her body was exhumed in 2007 for DNA testing, but none could be extracted because of its poor condition. After a second attempt was made in 2011 using better technology on bone material, a DNA profile was developed, police said Tuesday.
Associated Press writer Tom Hays contributed to this report.