UPDATED -- More details are surfacing about the driver in Friday's horrific train-truck crash in Nevada, including the possibility he may have been speeding.

About 11:25 a.m. Friday, a double-bottom dump rig plowed into the side of an Amtrak train at a crossing near Miriam, Nev. Six were killed in the fiery crash, including the truck driver, and dozens injured. One passenger remains unaccounted for after the crash.

The Associated Press reports that 43-year-old Lawrence R. Valli had received four speeding tickets since 2008. In one 10-month period, he had three citations for driving a school bus over the posted speed limit in California.

National Transportation Safety Board member Earl Weener said Valli was going "at a considerable speed" in a 70-mph zone before the crash. NTSB investigators are examining the truck's wheels, tires and brakes for details on the exact speed and the truck's braking capacity. The trucking company was permitted to haul oversize and overweight loads.

Valli's cell phone was recovered at the crash site and is being sent to NTSB's laboratory in Washington, D.C., where investigators will look into whether he was on the phone or preparing to send a text message at the time of the crash.

Valli had been working for John Davis Trucking Co. in Battle Mountain, Nev., for about six months and been a professional driver for 10 years, a family member told the AP.

The NTSB also will be looking at his employer, John Davis Trucking. According to published reports, the company has been cited for two crashes in the last two years, and was involved in a fatal single-vehicle accident last month. Much media attention has focused on the fact that the company had a truck put out of service for inadequate tread on the tires.

The company issued a statement, saying it wished to express "deepest condolences and sincerest sympathies to the family members and friends of those who lost their loved ones in the tragic accident of Friday, June 24. ... Please know that we recognize our moral and social obligation to find out how this accident happened, and we intend to cooperate with the authorities in their investigation."

The tractor, which was embedded in the side of the train, is being removed for examination. Investigators expect to find the engine control module, but say it was damaged in the fire and are unsure if they will be able to recover any data from it.

The NTSB originally said there were two co-workers in a three-truck convoy behind Valli, but changed that to one at a news conference Monday, noting that the driver was several vehicles behind.

Updated 5 p.m. EDT to add statement from John Davis Trucking.