Federal transportation officials released new details, including a simulation, from last year's deadly collision involving a semi and a Texas college softball team's bus.
On Tuesday, NTSB officials say a small pipe containing synthetic marijuana residue was found on driver Russell Staley. They allege Staley had a history of using the drug and didn't try to avoid hitting the bus in the opposite lane.
But a medical official says a blood test couldn't confirm the presence of the drugs in his system.
Staley is charged with four counts of first-degree manslaughter.