SALT LAKE CITY (AP) — The driver of a tour bus that crashed near a national park in Utah, killing four Chinese tourists and injuring dozens more, was making his first trip for a company that had only been in business for a short time, investigators said Sunday.

The National Transportation Safety Board is researching the driver’s background, license qualification and medical history, said Pete Kotowski, an investigator-in-charge for the agency, at a news conference Sunday night. He didn’t disclose the driver’s name but said he’s from California. The agency has not yet interviewed him.

The driver is a U.S. citizen and he didn’t appear to be intoxicated, the Utah Highway Patrol said previously.

The NTSB is also researching the bus company’s inspection history, hiring practices and corporate safety culture, Kotowski said. The company, called America Shengjia Inc., based in Ontario, California, is cooperating with investigators, he said.

Four people died and five others were in critical condition as of Saturday night. Hospital officials didn’t provide condition updates Sunday.