Eugene “Charlie” Martineau pleaded guilty to a reduced charge of manslaughter in the 2015 death of his 3-month-old son and will spend between 10 and 15 years in prison.

Martineau changed his plea from not guilty to a murder charge in Cumberland County District Court Wednesday morning. Prosecutors agreed to drop the murder charge against him in exchange for the guilty plea.

The lawyers could not agree on the length of Martineau’s sentence, so it will be up to a judge to decide. Martineau’s lawyers agreed not to ask for less than 10 years and prosecutors will not seek more than 15 and Martineau will be on probation for 12 years after he is released. The maximum sentence for manslaughter is 30 years.

Clifford Strike, Martineau’s lawyer, said the guilty plea was in recognition that the state probably had enough evidence to convict his client, but not an outright admission of guilt.

Martineau’s son, Leo Josephs, died in October 2015, three days after being admitted to the Maine Medical Center emergency room. According to prosecutors, an ER doctor described “a constellation of new and old injuries” to the infant, including massive retinal hemorrhaging, 24 rib fractures in various stages of healing, a broken ankle and a bad chest bruise.

Prosecutors said that Martineau told police investigating the death, “I hurt my son.”

According to the case outlined by prosecutors, Martineau was the sole caregiver for the infant, whose twin sister had been in the Maine Med neonatal intensive care unit since the babies were born 10 days prematurely in July.

They said the babies’ mother, Julia Josephs, walked four miles each way to work at a Hannaford store, where she put in around 25 hours a week, from their home in Sanford, where the couple lived in a house filled with other adults.

Some of those housemates told police that Martineau often yelled at the infant when the baby cried, prosecutors said, and he was seen striking the child hard on the back or roughly giving him a bottle of formula. The housemates said that they reported incidents to the state Department of Health and Human Services, but no record of any reports could be found.

Prosecutors said that Julia Josephs sometimes covered for Martineau’s rough treatment and impatience with the infant, saying injuries on the baby’s face were because a dog had been sitting on him.

Hospital personnel also said the parents rarely visited their daughter in the intensive care unit, prosecutors said, and Martineau learned a few days before his son was admitted to the ER with seizures that their daughter, Leah Josephs, was due to be released from the hospital soon.

Heather Gonzales, Martineau’s other lawyer, said Leah Josephs has been placed with her maternal grandparents, who are in the process of adopting the girl.

Strike said Martineau was “overwhelmed with two premature infants” and living in a room of a house crowded with other adults.

He said the prosecutor’s recitation of the evidence against Martineau “was a little overblown” and said he didn’t agree with some of the facts of the case presented by the state. He also pointed out that Martineau had no criminal history before being charged in the baby’s death.

Martineau’s mother, Anna Mercer, was in the courtroom for Wednesday’s hearing, occassionally sobbing. She left the courtroom immediately when the hearing ended and declined to be interviewed.

Martineau will be held in Cumberland County Jail until sentencing, which is tentatively set for May.