At 3:38 p.m. on Monday, March 26, 2018, a German tourist called the authorities from the Juan Creek crossing on California’s scenic Highway 1. She had spotted something jarring: a brown sport-utility vehicle, upside down, in the Pacific Ocean.

When Highway Patrol officers arrived, they found the S.U.V. Jennifer Hart was at the wheel, and her wife, Sarah Hart, was trapped between the roof and the seats in the back. Both were dead.

Within about three weeks, the authorities would also discover the remains of four of the Harts’ six children — Markis, 19, Jeremiah, 14, Abigail, 14, and Ciera, 12 — and declare them all dead, too. They eventually discovered skeletal remains inside a woman’s shoe, and announced this month that they belonged to 16-year-old Hannah. Devonte, 15, is still considered to be missing, but is presumed dead.

Jennifer, 38, had been drunk at the time of the crash, and Sarah, 38, and two of their children had in their systems a significant amount of an antihistamine that can cause drowsiness, law enforcement officials said.