Updated

Investigators scouring the area where a family of eight plunged to their deaths this week say they're still trying to figure out how the family's SUV careened off a California highway and fell to the rocky coastline below.

The wreck near Westport on the Pacific Coast Highway was discovered by a passing motorist Monday afternoon and its cause remains unsolved, though authorities are examining everything from how much gas was in the tank to credit card information in a bid to clear up “a lot of unknowns” surrounding the incident.

“We’re looking for everything,” Mendocino County Sheriff Tom Allman told SFGate. “Was there a pillowcase, a suitcase, who knows what?”

hart family california cliff crash

Investigators said the Hart family, seen here in 2016, is presumed dead after an SUV crashed off a cliff in California (AP)

Police said they have no reason so far to believe it was an intentional crash that claimed the lives of two women and at least three of their six adoptive children just days after Child Protective Services tried to contact the family over concerns about the kids' living conditions.

"There are a lot of unknowns on this," Allman said.

The women, Jennifer and Sarah Hart, both 38, were found dead inside the SUV, while three of their children — Markis, 19, Jeremiah, 14, and Abigail, 14 — were discovered outside the vehicle.

devonte hart

Devonte Hart, who was then 12, was photographed at a rally in Portland, Ore. in November 2014. (AP)

A team on Thursday continued to search the rugged coastline for the three other children, also believed to have been in the SUV and all presumed dead: Hannah Hart, 16, Sierra Hart, 12, and Devonte Hart, 15.

Investigators have said there were no signs of skid marks or of the GMC Yukon braking and the Alameda County Sheriff’s Office has been assisting in the search by sending a drone to videotape miles of the rugged coastline.

“Were they northbound, southbound, we don’t know the answer,” Allman said, according to SFGate. “That wreck could have happened two days before, or it could have happened an hour before it was reported.”

He added that police requested bank and credit card information to try to determine where the Washington state family was before the crash, and where they may have been heading.

california cliff 328a

Police are still trying to determine what caused the vehicle with the Hart family to plunge off the cliff. (AP)

The Associated Press reported investigators also are looking at factors such as brake failure, blown tires and weather. That model of Yukon was presumably equipped with a black box recorder that would show its speed and use of the brakes, said Marcus Mazza, an engineer and accident-reconstruction expert with Lancaster, Pennsylvania-based Robson Forensic.

Investigators can calculate the SUV's speed based on where it landed and the height of the drop.

"It's basic physics," Mazza told the Associated Press.

Family friend Max Ribner took issue with the notion it was something other than a tragic accident. The couple adopted children, many of whom came from "hard backgrounds" and "they transformed these kids' lives," he said.

One of the children, Devonte, drew national attention after the black youngster was photographed in tears, hugging a white police officer during a 2014 protest in Portland, Ore., over the deadly police shooting of a black man in Ferguson, Miss. Devonte was holding a "Free Hugs" sign.

Allman appealed to anyone who might have seen the family of eight to come forward.

On Friday, three days before their vehicle was found, Child Protective Services were called to the Hart house in Woodland, Wash., a small city outside Portland, Ore. where they moved to in May 2017, according to Oregon Live.

The Washington State Department of Social and Health Services had opened an investigation after the children were “identified as potential victims of alleged abuse or neglect,” Oregon Live reported, citing the Cowlitz County Sheriff’s Office. Bruce and Dana DeKalb, the next-door neighbors of the Harts in Woodland, told The Associated Press they called child services on Friday because they thought Devonte was going hungry. They said he had been coming over to their house too often in the past week asking for food.

Authorities attempted to reach the family three times since Friday, but couldn’t get in contact. The third attempt was made Tuesday, a day after their SUV was found. Signs showed the family planned for a short trip.

The agency had no prior history with the family.

The Associated Press contributed to this report.