Authorities said a body was recovered Saturday near the area where an SUV, believed to be carrying a family of 8, plunged off a North California cliff last month.
In a statement, the Mendocino County Sheriff's office said the body appears to be that of an African-American female.
Authorities have not been able to positively identify the body found on Saturday, but said the sheriff's office is "investigating the possibility that the body may be one of the two missing Hart girls".
An autopsy will be performed on the body on Tuesday, police said. Also killed were Markis, 19, Jeremiah, 14, and Abigail 14.
Investigators have said they believe the missing children - Devonte, 15, Hannah, 16, and Sierra, 12 - were inside the vehicle at the time of crash. The deaths also have raised suspicions about the motives of the two women, both white, in adopting black children.
Mendocino County Sheriff Tom Allman has described the crash as "a crime".
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"I'm to the point where I no longer am calling this an accident", Allman told HLN.
A fundraiser was set up to help a Penticton family who are dealing with the costs associated with transporting their dead son's body from Alberta.
Jennifer and Sarah Hart had adopted all six children and recently lived in Woodland, Washington.
Sarah Hart pleaded guilty in 2011 to a domestic assault charge in Minnesota over what she said was a spanking given to one of her children. Court documents there show that one of the couple's daughters had come to school with bruises on her back and stomach.
Neighbors of the Harts in Washington had called Child Protective Services, who opened an investigation, and the Harts left their home a day after officials tried to reach them there.