SYRACUSE - A woman accused of drowning a toddler in 2006 pleaded guilty to first-degree manslaughter Monday in a plea deal with St. Lawrence County prosecutors that requires her to plead guilty to the same charge for smothering her own baby in 1980.

Shirley Winters, 50, accepted a plea bargain Monday in connection with the death of 23-month-old Ryan Rivers. She originally faced a charge of second-degree murder for drowning the toddler in a bathtub at a Pierrepont residence in 2006.

She's to be sentenced on June 9 to 8 1/3 to 25 years in prison and five years post-release supervision, and is expected to spend at least 17 years in prison, said Assistant District Attorney Alexander Lesyk.

“I do believe she is a serial killer,” Lesyk said. “Do I think 20 years is enough? No.” But he said it was better to have a conviction than to risk going to trial on a circumstantial case.

Winters also is charged with the 1980 death of her own son in the Syracuse area. The plea bargain is tied to that murder charge in Onondaga County. She will plead to the same charge there and receive the same sentence, which will be served concurrently.

Onondaga County District Attorney William Fitzpatrick said he was satisfied with the agreement.

Winters was charged in March 2007 with smothering her son, Ronald Winters III - whose death was originally attributed to sudden infant death syndrome - after authorities exhumed the remains of the boy and two siblings killed in a suspicious 1979 fire in Jefferson County.

Investigators renewed their interest in the deaths of the Winters children after the Rivers drowning. The toddler drowned in the bathroom of his grandparents house while Winters was staying with the family.

In return for the two guilty pleas, Jefferson County officials agreed not to pursue charges related to the deaths of Winters' children Colleen, 3, and John, 20 months, in a fire at Hyde Lake, said public defender Brian Pilatzke.

Since 1979, Winters has been linked to 17 fires at homes where she lived or the homes of family members. She was convicted of arson in 1997 and served eight years in state prison for burning down her late mother's home. She also served time in state prison for assaulting a deputy.