Durham, N.C. — A truck driver charged in a crash last week that injured a Durham police officer suffered "a medical event" and wasn't drunk at the time, his attorney said Tuesday.

Charles Edward Caldwell, 44, of Roberta, Ga., is charged with felony serious injury by vehicle, driving while impaired, reckless endangering, speeding and unlawfully passing an emergency vehicle. He was released late Monday after posting a $500,000 bond.

Officer Teresa Gilliam had stopped a 2010 Mazda 3 last Wednesday afternoon on the right shoulder of Interstate 85 just past the exit ramp for Cole Mill Road, police said. A tractor-trailer then hit Gilliam's unmarked car from behind, forcing it into the Mazda.

Two truck drivers who saw the wreck said Caldwell's rig was weaving across lane lines before the crash and that, as they passed him, he appeared to be drunk or falling asleep at the wheel, according to an affidavit filed by police to obtain a warrant to search Caldwell's truck.

The search turned up a blue capsule on the floor of the truck cab, the warrant states.

Attorney Bill Thomas said the capsule was a generic decongestant.

Authorities who questioned Caldwell after the crash said he showed signs of impairment, including slurred speech and droopy eyes, according to documents. The North Carolina State Highway Patrol took a sample of his blood to test for alcohol or drugs.

Thomas said a blood analysis done at Duke University Hospital after the crash showed no drugs or alcohol in Caldwell's system, and he criticized the police for filing charges without checking on toxicology test results.

"The Durham Police Department has an unfortunate history of charging people with serious crimes without adequate investigation," said Thomas, who also represented a member of the Duke lacrosse team, which had three players falsely accused of rape in 2006.

Police spokeswoman Kammie Michael said the department had no comment about Thomas' statement, other than to note that Durham officers "are conducting a thorough investigation in this case."

Authorities said that, during questioning last Wednesday, Caldwell couldn't remember where his truck had been loaded earlier in the day, but he was clear on details of his trip until the crash, when he "suddenly couldn't clearly remember any details," documents state.

Caldwell has "an excellent driving record," Thomas said, noting that he has never been charged with DWI and hasn't had a speeding ticket in years.

The crash resulted from "a medical event," not an ongoing condition, he said, declining to elaborate.

Caldwell complained of chest pains while being questioned, and he was taken to Duke Hospital, where he remained until Monday.

Gilliam, a 15-year veteran of the Durham police force, was listed in fair condition Tuesday at Duke Hospital. Court records show she suffered brain and spine injuries and two broken ribs.