A 17-year-old mother who last year killed her 4-month-old child has pleaded guilty in Kailua, Kona to manslaughter.

Julia Aline Lewis waived Family Court jurisdiction Wednesday and agreed to be sentenced as an adult. She told the court that she suffers from depression and a bipolar condition.

She was 16 in October 2005 when she lived with her mother and her infant son on 'Olu'olu Street in Kona Highlands. The baby's father had moved to the Mainland to look for work.

Lewis was alone with her child, Sebastian Kossak, on Oct. 12, when police were called about 7 p.m. to investigate what initially was described as an accidental stabbing. They found the child dead with severe knife wounds to the neck.

Police charged Lewis with second-degree murder, but in a plea agreement brought to court this week, the charge was changed to manslaughter, still a Class A felony.

She will be sentenced Sept. 13 before Judge Elizabeth Strance. Supervising deputy prosecuting attorney Mel Fujino said the parties to the case have agreed to a sentence of up to one year in jail, 10 years' probation and restriction to a Mainland therapeutic institution until she is 21.

"This agreement considered the nature of the offense, the appropriate punishment, time allowed to address supervision, treatment for this defendant under Family Court or adult jurisdiction, the reports of court-approved mental health experts, and the safety of the community," Fujino said in a written statement.