A Carleton College student who was driving classmates to the airport when a crash killed three of them and injured another last year was found not guilty of two misdemeanor charges, a Dakota County judge has ruled.

The Dakota County attorney’s office failed to prove that William Shelton Sparks, 22, of Evanston, Ill., was guilty of careless driving and of failing to drive with due care, District Judge Colleen King ruled last week. Sparks had faced a possible 90-day jail sentence and/or $1,000 in fines.

A 1997 Toyota 4Runner driven by Sparks on Feb. 28, 2014, collided with a semitrailer truck on Hwy. 3 at County Road 47 in Dakota County, fewer than 3 miles from Carleton’s Northfield campus, after he lost control of the vehicle and skidded into oncoming traffic. The road was covered in ice and snow, according to the charges.

A crash reconstructionist from the State Patrol said Sparks’ speed in the conditions — estimated at 37 miles per hour in the 50-mph zone — was a factor. But a reconstructionist from the St. Paul Police Department said it was not a factor. The St. Paul police sergeant said he found no evidence that Sparks took any “unreasonable actions” that were “primary contributing factors for this collision.” There was no evidence of drugs, alcohol and distracted driving, according to court documents.

Killed were James P. Adams, 20, of St. Paul; Paxton M. Harvieux, 21, of Stillwater, and Michael D. Goodgame, 20, of Westport, Conn. Sparks and a passenger, Conor J. Eckert, of Seattle, then 19, were injured in the crash. They were all members of the school’s Ultimate Frisbee team, headed for a tournament in California.

The trucker was uninjured.

Sparks is continuing classes at the college, his attorney, Peter Wold, said Tuesday. Sparks suffered a brain injury, a broken arm and broken ribs in the crash, Wold said.

“Clearly this was an accident,” Wold said. “It’s perverse to try to turn that into a criminal [case].”

Last month, Sparks waived his right to trial on condition that both parties would agree on the facts of the case and submit arguments to King for a ruling.