The driver had multiple past violations, including driving a bus while his license was suspended. A witness says he believes the bus driver injured after the accident.
PHOTOS: Deadly tour bus crash on California's Highway 99
NTSB investigators say they will inspect the bus, highway, company, and driver. "This initial five to seven days is a fact-finding evolution," said NTSB senior investigator Don Karol.
The sheared open bus now sits in an evidence lot after the deadly accident on 3 a.m. Tuesday along Highway 99 in Livingston. CHP originally said five people died.
"I'm glad to say it's four rather than five. I wish it was zero," CHP Capt. Brian Hawkins said.
RELATED: Bus company in deadly crash has history of violations, problems
Jose Bustamante described hearing problems with the bus as it passed him on the highway. "Like clink, clink, clink, clink, clink," he said. Bustamante says he saw the bus driver Mario Vasquez helping passengers. "I heard him screaming, 'This is how you get out, lift up the handle, get out this way,'" he said.
But Bustamante says he later saw Vasquez on the ground. He says he believes the bus driver was hit by a passing car. He was taken to the hospital.
The California DMV confirms Vasquez has a history of driving violations including illegal/improper or unsafe change of lane in Washington on January 20, 2014, speeding 15 miles or more above the limit in Oregon on Oct. 23, 2014, and also a serious traffic violation in California that resulted in his license being suspended from Jan. 24, 2015 through March 24, 2015. And during that time, on Feb. 5, 2015, Vasquez was caught driving on the suspended license.
Investigators say the older model bus Vasquez Tuesday may not have had data recording capabilities. With or without that data, NTSB investigators will use a 3D laser to reconstruct the accident scene as part of the investigation.
Officials Wednesday released the identities of the four people who died. They're 68-year-old Jose Morales Bravo of Avalon, Calif.; 38-year-old Jaime de los Santos, 57-year-old Fernando Ramirez, and 64-year-old Petra Carillo Ruiz all from Mexico.
MORE: Driver ID'd as: Mario David Vasquez, 57 - still alive but major injuries. Hospitalized. Right now 5 dead, 6 airlifted @abc7newsbayarea— Jessica Castro (@JessicaABC7) August 2, 2016