Updated

The father of a Hawaii boy who went missing 20 years ago rode in a van with police and prosecutors last weekend, leading them to the site where he says he dumped his dead son's remains.

Peter Kema Sr., wearing a jail jumpsuit and shackles, went on the outing Sunday as part of a plea deal reached earlier this month, Hawaii County Prosecuting Attorney Mitch Roth said. Kema pleaded guilty to manslaughter in exchange for a 20-year sentence, on the condition that he reveal where the remains are.

The site in the Big Island's remote Puna district is in an area that police didn't previously search or consider, Roth said, declining to provide an exact location of where Kema says he disposed of the body.

The 6-year-old known as "Peter Boy," became the face of a Hawaii campaign for missing and abused children in the late 1990s and early 2000s. Posters and bumper stickers asked, "So where's Peter?"

Kema and his wife, Jaylin, have long been suspects in the boy's disappearance, but prosecutors said they didn't have enough evidence to charge them until last year, when a grand jury indicted the couple on murder charges.

Jaylin Kema pleaded guilty last year to manslaughter in the first official confirmation that the child was dead. In exchange for a one-year sentence with credit for time served, she agreed to waive her marital privilege and testify against her husband if he went to trial.

She agreed to facts prosecutors laid out in court about abuse suffered by the boy, her failure to get him medical treatment and his eventual death.

Prosecutors believe the boy died from septic shock from not getting medical care for an arm injury.

Peter Kema told authorities that he took his son from the Big Island to Oahu and gave him to someone named "Aunty Rose Makuakane" in an informal adoption. Police could not find a woman as described by Kema or airline records that indicated he had flown there.

If Peter Boy's remains can't be recovered, Kema must pass a polygraph test. Roth said it seems like Kema is being truthful about the location. "However, they lied for 20 years, so I'm cautiously optimistic," he said.

Police will later return to the site for a more detailed search. That will happen before Kema is sentenced in June, Roth said.

On Wednesday, Roth and police went to the site with Peter Boy's grandfather, brother, sister and an aunt. The relatives said prayers, lit candles and carried a lei for Peter Boy, Roth said.

On the drive there it suddenly rained, Roth recalled. "We talked about it being tears from heaven. It was like Peter Boy crying, 'they're finally coming for me,'" Roth said. "When we got to the scene, not a drop of rain. The sun came out."