(CNN) A fifth child from the Hart family, killed when their intoxicated adoptive mother drove the family off a California cliff last year, has been identified with the help of the girl's biological mother, police say.

She has been identified as 16-year-old Hannah Hart, the Mendocino County Sheriff's Office said in a Wednesday news release. One child, Devonte, 15, remains missing.

"The most likely scenario is that he, too, perished in this incident, but the case remains open and active," the sheriff's statement said.

Hannah's mom comes forward

Jennifer and Sarah Hart, both 38, adopted two sets of siblings: Devonte was brother to Jeremiah, 14, and Ciera, 12, while Hannah was the sister of Abigail, 14, and Markis, 19.

After Jennifer -- by all indications, intentionally -- drove the family off a cliff along US Highway 101 on March 26, authorities quickly identified the mothers, along with Markis, Jeremiah and Abigail. Two weeks later, Ciera's body was found on a beach north of the cliff.

Jennifer and Sarah Hart adopted two sets of siblings. Hannah stands on the far left.

The Mendocino County Sheriff's Office received a report May 9 that human remains -- part of a foot in a shoe, entangled in jeans -- had been found on a beach , but the crime lab could not immediately identify them.

"In October of 2018, a woman who identified herself as the mother of Markis, Abigail and Hannah Hart contacted the Mendocino County Sheriff's Office and indicated she had heard of this incident via a family member," the sheriff's statement said.

The woman provided a DNA sample, and on Tuesday, the crime lab informed investigators that the remains were those of Hannah.

An elaborate ruse?

Jennifer and Sarah Hart presented as the ultimate hippie moms , but in the weeks after their deaths, officials in Oregon, Washington and Minnesota, as well as people who knew them, said the homeschooling, organic food and music festivals were merely cover for their twisted philosophy on child rearing.

Among the allegations were that the Harts denied their kids food and forced them to lie on the floor for hours. Sometimes, punishment was meted out for behavior common among children, such as laughing at the dinner table.

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The details of what preceded the family's fate are not completely clear, but Bruce DeKalb, one of the family's neighbors in Woodland, Washington, said the family moved to the area between mid-2017 and early 2018. They were "very private," he said.

Shortly after they moved in, DeKalb said, one of the girls came to the DeKalbs' door at 1:30 a.m. requesting protection because her parents were mistreating her.

"We ended up getting her back to her parents ... and then I went over there the next morning and just checked on things, and everything seemed normal, and we let it go from there," he said.

Prelude to a tragedy

Days before the family's SUV was found at the bottom of the cliff, Devonte came over asking for food, saying his mothers had refused to feed him, as a form of punishment. Devonte continued coming over -- at first, once a day, but later as often as three times a day -- and the DeKalbs said they called Child Protective Services on March 23.

No one answered the door when a social worker dropped by, DeKalb said, and the family was gone the next day . Police found evidence they were in Newport, Oregon, and Fort Bragg, California, on March 24.

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The last sighting of the family came March 25, police said, when Jennifer Hart was seen on surveillance footage shopping at a Safeway in Fort Bragg.

After discovering the family's SUV, investigators said that Jennifer Hart's blood-alcohol content was over the legal limit to drive. Sarah Hart and some of the children were sedated when Jennifer got a 70-foot start and accelerated off the cliff without braking. There were no skid marks at the scene , police said.

"The Mendocino County Sheriff's Office is poised to follow up any viable investigative lead but has not received any indication of Devonte being located elsewhere," the department said Tuesday.