Get breaking news alerts and special reports. The news and stories that matter, delivered weekday mornings.

Washington sheriff's deputies have executed a search warrant at the home of the family who died after their car plunged over a California cliff.

The search is both an effort to gain insight into the deadly plunge — which may have been deliberate — and to possibly find three of the eight family members who still haven't been accounted for.

The affidavit, which was obtained by NBC News on Monday, shows that Clark County sheriff's deputies searched the home of Jennifer and Sarah Hart in Woodland, Washington, about 25 miles north of Portland, Oregon. They were seeking travel itineraries, bank and cellphone records and suicide notes, among other personal belongings, "to determine if the three outstanding children were involved in the collision or staying elsewhere."

The document is dated Friday, but it is unclear when the search occurred.

Jennifer and Sarah Hart, both 38, and their children Markis, 19, Jeremiah, 14, and Abigail, 14, were found dead at the crash site off Highway 1 in Mendocino County, on the north coast of California.

Let our news meet your inbox. The news and stories that matters, delivered weekday mornings. This site is protected by recaptcha

Three other children — Devonte, 15, Hannah, 16, and Sierra, 12 — haven't been found, but they are presumed dead, officials said.

Authorities said Sunday that the crash might have been intentional.

The affidavit says police were alerted to the crash just before 4 p.m. (7 p.m. ET) on March 26 when a German tourist reported a brown vehicle that was on its roof down an embankment.

Almost two hours later, according to the report, California Highway Patrol officers arrived and found Sarah Hart trapped between the roof and the rear seats of the family's GMC Yukon. Jennifer Hart was still in the driver's seat, with the speedometer "pinned" at 90 mph.

Officers said that meant the SUV was running and in motion before impact, but they said it was unclear how fast the vehicle was going when it crashed.

A Highway Patrol spokesman told reporters that the Yukon's on-board computer indicated that the vehicle stopped and then suddenly accelerated off the highway — plunging about 70 feet down to the rocky shoreline of the Pacific Ocean.

Three children were found ejected from the vehicle when police arrived, but as of Monday, Devonte, Hannah and Sierra still hadn't been found.

Devonte, a young black boy, was photographed in 2014 crying in the arms of a white police officer during a protest in Oregon over the police shooting of unarmed black teenager Michael Brown in Ferguson, Missouri. The image went viral and has been called the "hug that was felt around the world."

"Three children are still missing and could be in the ocean," Greg Baarts, acting assistant chief of the Highway Patrol, said Sunday. "We are trying to determine a timeline, path of travel, and if there were any stops."

The SUV of Jennifer and Sarah Hart was recovered off the Pacific Coast Highway, near Westport, California, on Wednesday. Alvin Jornada / The Press Democrat via AP

He said California authorities were "tirelessly searching for the missing children along the coastline," while authorities in California and Washington were "conducting interviews and attempting to establish a timeline and routes of travel in an effort to rule out any other possibilities."

The family had a troubled past, according to neighbors and court records. Sarah Hart was charged with misdemeanor domestic assault against her daughter Abigail in 2011, and Child Protective Services had visited the household.

Neighbors have said Devonte would ask them for food, saying his parents had withheld it as a punishment.