By Timothy Pratt

LAS VEGAS (Reuters) - The truck driver who plowed into an Amtrak train in Nevada, killing himself and at least five others last Friday, had received five traffic citations while driving commercial vehicles during the past three years.

Three of those tickets were issued to Lawrence Valli, 43, for speeding at the wheel of a school bus in California, according to Nevada Department of Motor Vehicles spokesman Kevin Malone.

Valli also was cited for driving without a seat belt in California and for driving over the speed limit in Alabama. All five citations occurred between July 2008 and September 2009, Malone said on Monday.

News of Valli's DMV record followed the revelation that the company which owned the tractor-trailer he was driving had been cited for seven violations stemming from random roadside inspections since September 2010.

But none of those cases involved the rig that slammed through railroad gates and into a passing Amtrak cross-country train early Friday, NTSB member Earl Weener told a news conference in Nevada on Sunday.

As of Monday, the official casualty toll from the fiery collision remained at six dead, including Valli and the train's conductor, with five other people missing and feared dead. Dozens more were injured.

At a briefing for reporters on Monday, Weener said the NTSB has recommended Amtrak use a system for tracking passengers similar to that of commercial airlines, making it easier to determine who is aboard in the event of an accident.

Weener also said a cell phone that may have belonged to Valli had been recovered from the scene, along with two minutes of video footage automatically taken by Amtrak trains when emergency brakes are activated. He said the video showed there were no obstructions on the track ahead of the train.

Valli's truck cab and the double trailer it was hauling weighed about 50,000 pounds in all and were traveling at such a high rate of speed at the time of the impact that the rig embedded itself in the side of the train.

The collision occurred at a railroad crossing at U.S. Route 95, about 70 miles east of Reno.

Forensic anthropologists were expected to join medical examiners on Monday as they continued to search for bodies in the second of two badly burned rail cars.

Investigators also will examine the driver's medical history, training record and experience, and NTSB officials will meet with the company on Tuesday, Weener said.

The NTSB reported earlier that the truck driver slammed on his brakes just 320 feet before the rail crossing, apparently failing to see signs, flashing lights and closed signal arms.

Initial inspections have found the crossing signal was set to activate 25 seconds prior to the train's arrival, and would have been visible from half a mile away to a truck traveling at the speed limit of 70 miles per hour.

Autopsy and toxicology results for Valli are expected to take a number of days. Weener said the NTSB would prepare a preliminary report within 30 days, but it may take a year for the agency to pinpoint a probable cause for the wreck.

(Editing by Steve Gorman and Jerry Norton)