(CNN) The mysterious California seaside crash in which at least five members of a family were killed is being labeled a crime by the man heading up the investigation.

Mendocino County Sheriff Tom Allman told HLN's "Crime & Justice with Ashleigh Banfield" on Wednesday that Jennifer Hart was driving her family's SUV when it went over a California cliff last week.

No one in the SUV was wearing a seatbelt, according to police.

"I'm to the point where I no longer am calling this an accident; I'm calling it a crime," Allman told HLN.

The sheriff said investigators were also looking at a cell phone found near the accident scene on the Northern California coast.

The bodies of Jennifer and Sarah Hart were found on March 26 inside the family's SUV, which had crashed at the rocky shoreline below a cliff. The bodies of three of their children -- Markis, 19, Jeremiah, 14, and Abigail, 14 -- were found nearby.

But their three other children -- Devonte, 15, Hannah, 16, and Sierra, 12 -- are missing, officials said. Investigators believe the missing children were inside the vehicle at the time of crash.

A large-scale search and rescue operation for the three missing children continued Wednesday, with about 80 people combing the surrounding area.

A tip led authorities to have divers search the water near the coastline about 30 or 40 miles south of the scene, but Allman said there was nothing yet to report from the search there.

Earlier Wednesday, the California Highway Patrol released a photo of Jennifer Hart shopping at a grocery store a day before her family's SUV plunged off a cliff.

Police also released a fuller timeline of the Hart family's movements before the fatal crash. The Hart family was in and around the Newport, Oregon area around 8:15 a.m. on March 24, and officials believe they then drove south along US 101 until they reached Leggett, California.

The family then traveled south along state Route 1 until they reached Fort Bragg around 8 p.m. that night, and remained there for about a day, police said. California Highway Patrol released an image from surveillance cameras of Jennifer Hart at a Safeway in Fort Bragg on the morning of March 25.

Jennifer Hart shops at a Safeway in Fort Bragg, California the day before her family's SUV plunged off a cliff.

No skid marks

Police had earlier said that several facts led them to believe the crash may have been intentional.

"At this point in our investigation, that is the direction we are going," said Greg Baarts of the California Highway Patrol's Northern Division.

There were no skid marks in the area leading up to the fatal crash.

And there were no witnesses to help guide police on what happened. The SUV was discovered only after a passerby saw the mangled wreckage at the foot of the cliff.

Data from the vehicle's software air bag module suggests the car had stopped at the scenic highway outcrop overlooking the cliff and then accelerated off the road, Baarts said.

Family's troubling history

Jennifer and Sarah Hart once lived in Minnesota, where Sarah Hart pleaded guilty to misdemeanor domestic assault involving one of the children in 2010, according to Douglas County court records.

That child had told an elementary school teacher of pain in her stomach and back, and bruises were discovered.

Sarah Hart told police she had spanked the child over the edge of the bathtub because of the child's behavior. She was sentenced to community service and one year of probation.

Then, about 10 months ago, the Harts moved into their home in Woodland, Washington, neighbor Bruce DeKalb said. He said the family was "very private."

Another neighbor, Bill Groener, said the children were home-schooled and kept inside most of the time.

DeKalb said Devonte and one of his sisters had told him they were being mistreated. The neighbor recalled two disturbing encounters he had with the children.

"One of the girls came to the door at 1:30 in the morning and said that she needed help and the parents were not treating her properly, and (she) wanted us to protect her," DeKalb said.

"We ended up getting her back to her parents ... and then I went over there the next morning and just checked on things, and everything seemed normal, and we let it go from there."

In 2014, Devonte garnered national attention when he embraced a white police officer at a time when racially charged protests were being held across the country, following a grand jury's decision not to indict the white officer who killed Michael Brown, an unarmed black man.

Devonte helped quell tensions with his sign offering "Free Hugs," and his photo was shared around the world.

Update: This story has been updated to include new information from police. Police now say Sarah and Jennifer Hart were not wearing seatbelts as previously reported.