Updated

The driver of a bus that crashed last year in Virginia, killing four passengers and injuring dozens more, was convicted Thursday of involuntary manslaughter.

Caroline County Circuit Judge Joseph Ellis told Kin Yiu Cheung on Thursday that the driver's conduct was "so gross and wanton," that the judge had no choice but to find him guilty of all four counts of involuntary manslaughter that he faced.

Caroline County prosecutors called 15 witnesses, including several passengers on the low-fare Sky Express bus from Greensboro, N.C., to New York.

They described erratic driving, including weaving and repeatedly speeding up and slowing down, before the bus swerved off the road, hit an embankment and overturned. The crash happened in May 2011 on Interstate 95 about 30 miles north of Richmond.

"It was like a nightmare. I remember it like it was yesterday," passenger Andrew Jennings testified. "I woke up to people screaming, the bus was flipping, it was completely dark."

A state trooper testified that Cheung nodded when asked whether he'd fallen asleep behind the wheel.

Commonwealth's Attorney Tony Spencer pointed at Cheung and said, "That man had a legal duty of care to those passengers, and that's a factor in this case."

Cheung's attorney, Taylor Stone, called the crash a "horrendous accident," and argued it "doesn't rise to the standard of criminal negligence."

Cheung faces up to 40 years in prison at his sentencing Jan. 23.