SCHENECTADY - In a plea deal that will potentially cut decades off her prison time, Heaven Puleski admitted Thursday she killed her infant son last summer.

Under the deal offered by the Schenectady County District Attorney's office, Puleski admitted killing her three-month-old son, Rayen, before discarding his body in a plastic bag in a sewer behind her State Street home.

Puleski's plea to first-degree manslaughter comes with a promised sentence of 15 years in state prison. She will be sentenced June 5.

She had faced a top count of second-degree murder, an offense that carries a maximum penalty of 25 years to life in prison.

If convicted of that charge, Puleski would have needed the approval of a state parole board before she could get out of prison.

Puleski appeared Thursday with her defense attorney Lara Barnett in front of County Judge Matthew Sypniewski. Barnett did not return a call Thursday seeking comment.

Rayen vanished last summer and relatives went to authorities, fearing for the child's safety. Child Protective Services contacted police.

The boy's body was found Aug. 10 behind 766 State St., the apartment building where Puleski had been living with the child after moving from Saratoga County earlier in the summer.

In August, Puleski was arrested after police found Rayen's body in a hole that led to an underground sewer tunnel.

A grand jury indicted Puleski in October.

At the time of the indictment, county prosecutors said the baby suffered injuries during "violent shaking and throwing" by Puleski.

District Attorney Robert Carney said afterward they had an eyewitness to that even though Puleski's story is that she was strung out on heroin, slept in the same bed with the baby, and woke up to find the baby dead.

Carney said his office agreed to the plea deal because the child's body was so badly decomposed that investigators could not determine a cause of death.

"The primary problem is that we could not prove the cause of death medically," he said, adding that "at the time the remains were found they were greatly deteriorated."

As a result, his office enlisted the help of an FBI anthropologist and a local forensic pathologist.

He said Rayen was killed around July 18 and that his body was discovered about three weeks later.

The DA also said that the prison term assures Puleski, 38, will be beyond her child-bearing years when she gets out. When that happens, Puleski will be on post-release supervision for five years.

Rayen had been under the supervision of Child Protective Services in Saratoga County. Schenectady County's child protective workers took on the case when Puleski moved there.