The attorney representing a Santa Clara County sheriff's deputy who struck and killed two competitive bicyclists in Cupertino said Wednesday that the officer had worked a lengthy shift the day before and that fatigue may have been a factor in the crash.

She would not confirm witness reports that the deputy, 27-year-old James Council, told people at the crash scene Sunday morning that he had fallen asleep at the wheel. Council "doesn't know what happened" when he veered across the center line of winding, two-lane Stevens Canyon Road, killing the two cyclists and injuring a third, attorney Mary Sansen said.

"The possibility exists," she said, "that we're never going to know what happened."

Two men who came upon the accident scene a short time after the crash said Council had said he thought he fell asleep. Since then, Council has not spoken, publicly or to investigators.

Sansen said in a lengthy interview in her Pleasant Hill office that prosecutors who must decide what charges, if any, to file in the case may need to look at Council's work schedule before the crash.

Council was 4 1/2 hours into a 12 1/2-hour shift when the accident occurred at 10:25 a.m. Sunday. He worked a 6 a.m.-to-6:30 p.m. shift on Saturday, the sheriff's office said, meaning that with the switch to daylight-saving time Sunday, Council had 10 1/2 hours off between shifts.

"A 12 1/2-hour shift is brutal," said Sansen, who specializes in representing law enforcement officers. "You're not sitting behind a desk. Even if you don't work in a high-crime area, you're always on alert for 12 1/2 hours. It is exhausting."

She added, "Nobody goes home at the end of a 12 1/2-hour shift and goes right to bed."