ALBEMARLE COUNTY, Va. (WVIR) - Ever since charges were first filed in connection with an Amtrak and truck collision that occurred earlier this year in Crozet, prosecutors suspected that the trash truck driver was driving under the influence.

But now there's proof that the driver was in fact under the influence.

Court documents show that 31-year-old Dana Naylor, who was the driver in the January accident, had THC - the psychoactive component from marijuana - in his system on the day of the crash.

A medical expert says Naylor's test didn't just come back positive, but that the levels were also elevated.

A collision between a trash truck and a GOP congressional train on January 31 took the life of one man in the trash truck and permanently injured another.

Naylor was indicted for manslaughter and DUI maiming.

Documents show that his urine tested positive for THC at a 606 level at the time of that deadly accident.

“It's certainly gonna make a screening test positive, which makes them do a confirmation test, right?” Dr. Chris Holstege, a medical doctor with the University of Virginia’s School of Medicine, said. “It's above what the cut-offs typically are for screenings, so now I have a level that's elevated, and significantly so."

Holstege says there's no question marijuana was in the driver's system at the time of the accident.

“They certainly did marijuana,” Holstege said. “The question then comes - how often marijuana? If you're a chronic user, that can impact your driving, right?"

However, there is no target number for THC like there is with alcohol content in the body.

That gap in the law makes it hard to say whether or not the driver could have been impaired at the time of the crash.

“It's hard to interpret, and especially from urine to go back and say 'yes that level’s really high, that must have meant that they were inebriated at the time of the accident,'” Holstege said. “You really can't do that."

NBC29 reached out to Naylor's attorney and the commonwealth about these findings, but neither would comment on the pending case.