DNA testing confirmed partial human remains found on a Mendocino County beach belonged to 16-year-old Hannah Hart, who was killed nine months ago when a vehicle driven by one of her adoptive mothers and carrying their entire family of eight plunged off a seaside cliff, authorities said Wednesday.

Investigators have been trying to identify the remains — a skeletal foot found inside a shoe that was tangled in a pair of girl’s jeans — since May when it washed ashore at Hardy Creek about a mile north of the crash site.

Initial DNA testing was inconclusive, but in October the girl’s biological mother contacted Mendocino County law enforcement after learning about the fate of her daughter, who had been adopted by Jennifer and Sarah Hart, most recently of Woodland, Washington.

The deadly crash on the Mendocino Coast revealed troubling details about how the Hart women treated their six adopted children and the ineffective child welfare systems that failed to protect them.

The family had been the focus of child welfare investigations in multiple states as the family moved around the country.

In one incident, Hannah Hart jumped out of a second-floor window in November 2017 when they lived in Woodland and went to a neighbor’s home to ask them to rescue her from her mothers.

But on March 26, the family’s eight-seat GMC Yukon XL was spotted upside down in the surf at the bottom of a cliff on the Mendocino Coast near Westport.

Investigators believe Jennifer Hart, 38, intentionally drove the family’s SUV off the 100-foot cliff along a Highway 1 turnout near Westport, killing her family.

She was legally drunk at the time of the crash, and lab results showed her wife and at least two children had ingested sedatives.

The Hart women were found dead inside the SUV, as were three of their children — Markis Hart, 19, Jeremiah Hart, 14, and Abigail Hart, 14.

But authorities did not immediately recover the bodies of Hannah Hart, her 12-year-old sister, Ciera Hart, and 15-year-old brother, Devonte Hart.

Ciera’s body was found in coastal waters in April and identified using DNA.

Devonte Hart is still classified as missing. He is presumed to have died but his body has not been found.

You can reach Staff Writer Julie Johnson at 707-521-5220 or julie.johnson@pressdemocrat.com. On Twitter @jjpressdem.