Police say human remains found along a Northern California beach have been identified as those of one of six adopted children presumed dead last spring after a woman intentionally drove the family's SUV off a cliff, The Associated Press reports. The Mendocino County sheriff’s department said the remains were identified as those of 16-year-old Hannah Hart after her biological mother contacted the police department from Alabama. Authorities found the remains shortly after the Mar. 26 car crash. Police believe the teen's adoptive mother, Jennifer Hart, was drunk when she purposefully drove her car off California’s Highway 1 about 150 miles north of San Francisco. Hannah, six other children aged 12 through 19, and Jennifer's wife were reportedly found with large amounts of a drowsiness-inducing drug in their systems. Investigators are still trying to determine a motive for the crash. The remains of 15-year-old Devonte Hart have not yet been found, and he remains the only child left unaccounted for.