Ten days after a big moving van caught fire in East Texas, authorities are still trying to figure out who packed an estimated $1 million cash in the trailer.

Tragically, the driver of the Atlas Van Lines 18-wheeler, Eric Royster of North Carolina, was struck and killed as he stood near the burning truck, apparently taking cell phone photos, said Lt. Jay Webb of the Harrison County Sheriff's Office.

A good chunk of the cash burned up in the fire that broke out about 4 a.m. Dec. 2 when the truck was westbound on Interstate 20 near the Louisiana border, Webb said.

The fire was caused by the trailer brakes catching, which created friction. When the driver and co-driver realized the brakes were overheated, they stopped, and flames erupted immediately, he said.

According to information from the co-driver, the two jumped out and separated the tractor from the trailer. The 18-wheeler driver was standing in the roadway of adjacent U.S. Highway 80 when he was struck, Webb said.

Authorities don't know if the driver had any idea the bundles of cash were in the rear of the trailer, which carried two loads of household furniture and was headed westbound to Kingman, Ariz., and then to California.

In addition to the sheriff's office, the case is also being investigated by the Texas Department of Public Safety and the U.S. Drug Enforcement Administration, Webb said.

Judging by the way the cash was stacked and wrapped in plastic and then overwrapped in aluminum foil, it appears it was intended to pay for illicit drugs, he said.

"We would love to be able to say we stopped a delivery of drug money, and we believe we did," he said.

While news reports have stated that the sheriff's office retrieved about $1 million from the truck, that is an estimate of what the original amount might have been, he said.

"We have $250,000 that we can say is viable currency," he said Friday. "Other (cash) is parts and pieces in various stages of being singed and burned."

The $250,000, which is intact but cannot be returned to circulation, was given to a local commercial bank, which sent it to the Federal Reserve Bank of Dallas, Webb said.

When the money arrived at the Dallas facility, however, officials determined it was too badly burned to be processed by machines there, a spokesman said Friday by email.

The money was then returned to the commercial bank in Harrison County with instructions to send it to the U.S. Treasury Department for processing, reserve bank spokesman Alex Johnson said.

Another four "grocery bags" of burned currency fragments were sent to the U.S. Bureau of Engraving in Washington, DC, where it could take as long as three years to determine the face value of the debris, Webb said.