WATKINS GLEN, N.Y. The sheriff in charge of investigating Saturday night's crash in which NASCAR star Tony Stewart hit and killed a sprint car driver standing on the track said there is no evidence so far to file criminal charges against Stewart.

But Ontario County Sheriff Philip Povero said Sunday that his department continues to gather information, asking fans who were at the race to turn over video of the crash that killed 20-year-old Kevin Ward Jr. of Port Leyden, N.Y.

A shaken Stewart withdrew from Sunday's NASCAR race at Watkins Glen International and released a statement, saying:

"There aren't words to describe the sadness I feel about the accident that took the life of Kevin Ward Jr. It's a very emotional time for all involved, and it is the reason I've decided not to participate in today's race at Watkins Glen. My thoughts and prayers are with his family, friends and everyone affected by this tragedy."

The fatal crash was one of the most unusual in decades involving two drivers.

A sprint car driven by Stewart struck and killed Ward, who was standing on the dirt track while Saturday night's race at Canandaigua (N.Y.) Motorsports Park was under caution. Stewart's and Ward's cars had tangled 25 seconds earlier, sending Ward into an outside wall.

Ward got out of his car, stepped quickly toward the infield and stood in the middle of the track, pointing in what appeared to be an accusatory way toward Stewart's car coming toward him. One other car narrowly missed Ward.

As Stewart approached, his car appeared to speed up. Then the right of Stewart's car, possibly his rear tire, hit Ward, knocking him several yards down the track. Ward was pronounced dead on arrival at F.F. Thompson Hospital in Canandaigua.

H.A. "Humpy" Wheeler, former president of Charlotte Motor Speedway, said that in his 50 years of watching races, he can't recall another time when a race car struck a driver who had left his car. Usually, he said, drivers don't immediately get out of their cars after wrecks.

He said there are no rules in auto racing prohibiting drivers from leaving their cars immediately after wrecks. But he said he wouldn't be surprised to see that change as a result of Ward's death.

Povero, who estimated Stewart's speed at about 35 mph at the time of the crash, said authorities questioned Stewart at the scene. They found him cooperative and "very upset" about the incident.

Investigators are examining the track and the lighting, talking to eyewitnesses and interviewing people who have experience in sprint car racing, Povero said.

Steve Ward, a retired Mecklenburg County prosecutor, said authorities would likely be hard pressed to prove that Stewart intentionally tried to kill or scare Kevin Ward, given that the young driver walked into the middle of the track and that another car almost hit him right before Stewart did.

"When you jump out of the race car and get out in the groove, you're putting yourself in all kinds of danger," Wheeler said. "What was going through Tony's mind, no one will ever know but Tony. Certainly the last thing in the world he wanted was to hit another driver."

In recent weeks, Stewart, 43, has returned to dirt track racing after breaking two bones in his right leg in a wreck at a dirt track in Iowa last summer.

Even after earning the opportunity to compete in racing's big leagues, such as the IndyCar Series and NASCAR Sprint Cup Series, Stewart has continued to compete at dirt tracks across the country.

"Everybody has hobbies. Everybody has stuff they like to do when they have downtime, and that's just what it is for me," Stewart said last month. "That's what I like to do when I have extra time. I don't think there is anything wrong with doing it."

Nothing makes a driver's adrenaline pump more than sprint car racing, Wheeler said. Cars packing 900 to 1,000 horsepower hurtle down short, slick dirt tracks as they have for decades on Saturday nights in the Carolinas and throughout the South.

"It's exactly like driving real fast on hard-packed snow," Wheeler said. "And there are some wild cowboys out there. ... It's just controlled mayhem."