MORRISTOWN, N.J. -- The mother of a newborn girl whose body was found in a New Jersey park on Christmas Eve nearly 40 years ago has been identified and is now charged in the death, authorities announced Thursday.

The infant, dubbed “Baby Mary” by a police chaplain, was found by two young boys in a secluded park in Mendham Township in 1984, Morris County Prosecutor Robert Carrol said. The child's umbilical cord was still attached when she was found, and she was wrapped inside a towel inside of a plastic bag. She was alive when she was abandoned, Carrol said.

The woman, who was 17 at the time, was arrested in South Carolina on April 24 and charged as a juvenile with manslaughter. She is not in custody but is “being monitored,” Carroll said.

The woman's name was not released since she was a juvenile when the death occurred. The identity of the child’s father — who was 19 at the time — was also determined, Carroll said, but authorities said he was unaware the baby had been born and he was not involved in her death. He died in 2009.

A possible motive or reason for abandoning the baby has not been disclosed.

A breakthrough in the case came several years ago when a DNA match between the infant and the father was made, Carroll said, though he declined further comment.