After 20 years, what happened to “Peter Boy” Kema may finally be revealed when his mother testifies against the boy’s father, who is scheduled to stand trial in April for murder in the disappearance of the then-6-year-old Hawaii island boy. His mother, Jaylin Kema, pleaded guilty to manslaughter Thursday.

In a case that galvanized Hawaii, the face of the abused boy and the message “So where’s Peter?” can still be seen on faded orange-and-black bumper stickers around the Big Island.

Peter Boy Kema, who suffered from repeated physical abuse, disappeared in the spring or summer of 1997.

Prosecutors say they believe Jaylin Kema doesn’t know where the body is, and that the boy died from septic shock from not getting medical care.

In exchange for her testimony, prosecutors recommend a one-year sentence, with credit for time already served. If the trial isn’t over by April, she’ll be on supervised release, according to the plea agreement.

Hawaii County Prosecutor Mitch Roth on Thursday thanked police, prosecution investigators, Kema family members and the public at large for continuing to push for justice.

“I’m so proud of the people of the Big Island for never letting this case fall from memory,” Roth told the Honolulu Star-Advertiser. “The big things are that we know what happened to Peter Boy.”

But Roth demurred when asked whether he knows how Peter Boy Kema died and what happened to his body.

Instead, Roth said repeatedly that he did not want to jeopardize the case against Peter Kema Sr., who is scheduled to go on trial in April on a charge of second-degree murder.

“We’ve still got one more case to put this to a closing,” Roth said. “There’s a lot of things that people should know.”

Without being specific, Roth expressed confidence in the case against Peter Kema Sr.

“We have an ethical duty not to charge cases unless we believe that we can prove it beyond a reasonable doubt,” Roth said. “That’s why we went forward.”

Peter Kema Sr.’s Hilo attorney, Stanton Oshiro, did not respond to a request for comment. Nor did Hilo attorneys for Jaylin Kema.

The big break in the case came Thursday in Hilo. After years of denying any involvement in the boy’s disappearance, Jaylin Kema pleaded guilty to manslaughter in her son’s death and agreed to testify against her husband.

Peter Boy’s parents have been held separately in custody after they were charged in April with second-degree murder following an indictment by a Hilo grand jury.

Roth suggested that the couple’s separation “may have played a role” in getting Jaylin Kema to change her plea from second-degree murder to manslaughter in exchange for testifying against her husband.

“Just having them apart may have given her time to think for herself,” Roth said.

She likely will not be sentenced until May, Roth said, and faces a year in jail and 10 years’ probation.

Peter Kema Sr. faces the possibility of life in prison without parole.

The parents separated in 2005, and Jaylin Kema obtained a restraining order that year against her husband, saying in court papers that he had been abusive.

The state Department of Human Services previously released 2,000 pages of confidential documents that revealed, among other things, that Peter Boy Kema’s then-5-year-old sister told a psychologist that she had seen her brother’s dead body in 1998 on two occasions.

A team of child-welfare advocates also said in 1998 that they believed the parents may have been responsible for his disappearance, according to the DHS documents.

The Associated Press reported Thursday that Hawaii County Deputy Prosecuting Attorney Ricky Damerville said Jaylin Kema agreed in court to facts he laid out about abuse the boy suffered, her failure to get him medical treatment and his eventual death.

In 1996 and 1997 extended-family members, most of them now dead, were concerned the boy’s father was abusing him. An arm injury was left untreated, festering and filling with pus until there was a hole so deep someone could put a finger inside it, Damerville said.

Despite having health insurance, Jaylin Kema didn’t get her son medical treatment and didn’t report the abuse because she was afraid of her husband, Damerville said.

“I failed to protect my son,” she said, crying as Damerville read the details in court, KHON-TV reported.

Sometime between May and June 1997, the couple’s then 4-year-old daughter heard Kema calling out for her husband and saw her trying to resuscitate the boy. She later saw her brother in a box, Damerville said.

Peter Kema Sr. told authorities in August 1997 that he left Peter Boy with a longtime family friend, “Aunty Rose Makuakane,” at Aala Park in downtown Honolulu while looking for a job on Oahu. The existence of “Aunty Rose” could not be verified.

The boy’s disappearance initially was considered a missing-person case but was reclassified as a homicide in 2000, although no arrests had been made.

During his 2012 campaign for Hawaii County prosecutor, Roth pledged to review the island’s unsolved cases, including Peter Boy Kema’s.

Roth said that indictments in other unsolved murder cases could be forthcoming in the next few months.

“Four years ago we decided we would look at these cases with a fresh set of eyes,” Roth said. “We haven’t forgotten about these cases. The family doesn’t forget. The community shouldn’t forget, either. We want to make sure that justice prevails.”

Jaylin Kema originally was charged with second-degree murder “based on an omission,” Roth said. “As a mother of a child, you have a duty to act when your child needs medical care, and she failed to act.”

In an agreement with the prosecutor’s office, she pleaded guilty to manslaughter and to a charge of second-degree theft in connection with a welfare fraud case.

Prosecutors previously said Kema collected more than $17,000 in public assistance benefits she wasn’t entitled to between May 2010 and July 2015. The theft was uncovered because of the murder investigation, prosecutors had said.

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The Associated Press contributed to this report.