SPARKS, Nev. -- A Nevada trucking company under scrutiny for a fiery crash with an Amtrak train that left at least six dead has been cited repeatedly by state authorities for crashes, unsafe driving and operating a truck with tires so bald the vehicle had to be taken off the road.

A man working for John Davis Trucking Co., of Battle Mountain, Nev., drove a truck through a crossing gate's housing unit and into two of the train's double-decker cars Friday, killing him and five people on the train.

Federal records reviewed by The Associated Press on Sunday showed the state Department of Public Safety cited the company for two crashes in the last two years, including one in February 2010 that injured a person in Washoe County.

In a January inspection, authorities found tires on one company tractor-trailer so bald they deemed the rig an imminent hazard to public safety.

National Transportation Safety Board member Earl Weener told reporters Sunday night that it was difficult to say whether the company's record was significant or atypical in the industry.

Meanwhile, Amtrak spokeswoman Vernae Graham told the AP that five passengers who were on the train's manifest of more than 200 people remained unaccounted for after the crash.

More than two dozen people were sought a day earlier, but Weener said some of them may have gotten off the train before the crash or walked away from the scene without checking with officials.

"This is not quite like you are used to when you get on an airplane. They record exactly who gets on, and what seat they sit in," he said. "On a train, you can get off without necessarily being tracked."

The truck driver, a conductor and four others on the train were killed in the wreck in which a semi-trailer truck slammed into two passenger cars 70 miles east of Reno.

Churchill County coroner officials sifted through the rubble of the rail cars gutted by the fire, and investigators said they found no additional victims Sunday.

At least one forensic anthropologist has been asked to assist, said Nevada Highway Patrol Trooper Chuck Allen.

"I think it was so hot that they want to make sure they are not missing anything," Allen told the AP. "They want to figure out if there are any more bodies and if so, how many. They want to rule out the possibility that, yes there are more, or that no, there are not."

Investigators also looked for clues as to why the truck driver plowed through the railroad crossing, but Weener said examining the truck tractor has been difficult because part of it remained stuck in a rail car.
It's expected to take up to a year to pinpoint the cause of the crash.

"Just from handling or being on the scene of so many accidents, there are so many alternatives to consider," Allen said.

"Not necessarily just drugs or alcohol, but fatigue, driver inattention," Allen said. "Did he have a (citizen band radio)? Was he talking to his buddies behind him? If so, was he looking in the side-view mirror and not looking at the road ahead? I don't think we'll ever know for sure."

Autopsies on the victims were expected within the next few days, with toxicology test results on the truck diver due a few days after that.

Weener said that the flashing lights at the crossing, which are set to blink for 25 seconds before a train approaches, would have been visible from a half-mile away if a motorist was driving at the highway's 70-mph speed limit.

More than two days after the accident, a variety of factors remained unknown, including how fast the driver, whose name has not been released, might have been going as he approached the tracks from the south, Weener said.

Two other truck drivers and the train's engineer watched helplessly as the semitrailer skidded the length of a football field before crashing into the train.

The drivers were part of a three-truck convoy that saw the gates come down and the warning lights go off as the California Zephyr approached, Weener said.

They stopped, but the driver of the big rig in the lead did not, he said.

The train's engineer saw the truck approaching the crossing and realized the collision was inevitable, he said. The engineer slammed on the emergency brakes, but the train, which was going about 78 mph in an 80-mph zone, traveled a half-mile more before it finally stopped, Weener said.

The engineer watched the truck smash into two of the train's 10 cars through the rearview mirror.

"He recalled the event clearly. He saw the truck approaching the train," Weener said late Saturday. "At some point, he knew the impact was imminent. He, in fact, watched the collision in a rearview mirror. He was hoping the train was not going to derail."

Weener said investigators would meet with the trucking company on Tuesday and review the driver's medical history, training and experience. He also has said the driver's professional commercial driving record "is an area we will be taking a very close look at."

John Davis has 67 trucks and 130 drivers who drove nearly 4 million miles within Nevada state lines in 2008, according to the most recent data available from an inspection and crashes database from the Federal Motor Carrier Safety Administration.

The trucking company's website describes it as family-owned, with more than 100 vehicles and a concrete plant, and specializing in hauling sand, gravel, and ore from the local mines. The company did not immediately return a call or email Sunday.

On Jan. 19, during a roadside inspection, state authorities found exposed tire treads on one of the company's tractor-trailers and ordered it off the road immediately, records show.

In the last two years, state authorities also cited the company for 16 other vehicle maintenance violations, including oil leaks and inoperative lamps, but no others were deemed sufficiently serious to order the vehicle off the road.

Weener said the company had received seven violations since 2010 and that one of them forced a truck to be taken out of service, but he provided no other details.

On Feb. 3, 2010, the Nevada Highway Patrol reported a company tractor-trailer driver got in a crash in Washoe County that left one person injured, and either one or both of the vehicles was towed.

On Oct. 29, 2009, crash reports showed another company driver got in a wreck in Humboldt County, in which one or both of the vehicles had to be towed.

Overall, large-truck crashes in Nevada caused 199 injuries last year, but federal records don't detail who was at fault.

At a roadside inspection on Feb. 22, inspectors cited a John Davis driver for failing to use a seat belt and for an equipment defect on the rig's hydraulic brake system. In another on April 5, 2010, Nevada authorities cited another driver for lane restriction violations.

The company also was cited for cargo violations that included prohibited hazardous material markings on packages one driver was carrying and labeling problems, the records showed.

Allen said it was not unusual for state public safety officials doing spot roadside inspections to take trucks out of service for unsafe driving practices of discrepancies in travel logs.

He said he wasn't familiar with the trucking company's record but said that "having just a couple of tickets, I don't think is an alarming issue."