YONKERS, N.Y. (CBSNewYork) — A common law couple have pleaded guilty in connection with the death of their 6-month-old child, the Westchester District Attorney’s Office said.

Clarence Thomas, of Yonkers, pleaded guilty to second-degree manslaughter in the death of his daughter Natalia Johns. The DA’s office said the girl’s mother, Kayan Johns, also pleaded guilty to one count of endangering the welfare of a child.

According to prosecutors, around 6 a.m. on March 14, 2013 Johns called 911 and reported her daughter had stopped breathing.

When emergency responders arrived at the home, the child did not have a pulse, prosecutors said. She was rushed to St. Joseph’s Medical Center in Yonkers and pronounced dead at 7:14 a.m.

Following an autopsy, the Westchester County Medical Examiner’s Office said the child had numerous injuries consistent with both old and new trauma to the head.

Police questioned Thomas, who prosecutors said gave various accounts of how Natalia could have sustained the injuries.

Prosecutors said Kayan Johns, of the Bronx, had noticed the injuries and bruising on her daughter, but did not report it or seek medical attention. They said she also continued to allow Thomas to watch Natalia and their other children while she worked.

“These parents, the father by his reckless actions and the mother by her denial of any abuse, tragically led to the death of their six month old daughter. A parent’s primary job is the care and protection of their children and in this case their inability to do so led to this terrible outcome,” said District Attorney Janet DiFiore. “Thus, it now becomes incumbent on society and the criminal justice system to make sure that they are held accountable.”

The couple is expected to be sentenced on May 12. Thomas faces up to 15 years in prison if convicted.