Story highlights "All options remain available," sheriff says

Video shows Stewart's car hitting Kevin Ward Jr. as he walked on track near vehicle

Tony Stewart says he can't describe how sad he is after the accident

Although NASCAR driver Tony Stewart is not currently facing criminal charges in the death of another driver, he is not officially in the clear.

"This is an ongoing investigation, and all options remain available," Sheriff Philip C. Povero of Ontario County, New York, said Monday. "We're continuing to gather and analyze every piece of evidence we can."

Stewart hit and killed another driver who was walking on a track during a dirt-track race in upstate New York on Saturday night, authorities said.

Kevin Ward Jr., 20, died from injuries suffered in the incident at the Empire Super Sprints series event at the Canandaigua Motorsports Park.

The track is about a two-hour drive from Watkins Glen International race track, where Stewart had been scheduled to race in a NASCAR event Sunday.

"There aren't words to describe the sadness I feel about the accident that took the life of Kevin Ward Jr.," Stewart said Sunday, according to a written statement tweeted by NASCAR. "It's a very emotional time for all involved. ... My thoughts and prayers are with his family, friends and everyone affected by this tragedy."

Stewart decided not to take part in Sunday's event.

"Our hearts go out to Kevin's family," said Stewart's team director, Greg Zipadelli. "This is a very tough, very emotional time for everybody -- his family, our family at Stewart-Haas Racing."

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Photos: Racer Tony Stewart Photos: Racer Tony Stewart – NASCAR driver Tony Stewart looks on in the garage area during practice for a race in Watkins Glen, New York, on Friday, August 8. Stewart is a three-time champion in NASCAR's top division. Hide Caption 1 of 13 Photos: Racer Tony Stewart Stewart signs autographs for fans during a practice in Loudon, New Hampshire, in July 2014. Hide Caption 2 of 13 Photos: Racer Tony Stewart Stewart gets out of his car after a crash in Daytona Beach, Florida, in July 2014. Hide Caption 3 of 13 Photos: Racer Tony Stewart Stewart and Danica Patrick ride down pit road before a race in Brooklyn, Michigan, in June 2014. Hide Caption 4 of 13 Photos: Racer Tony Stewart Stewart poses with a rifle awarded to him after qualifying for pole position at a race in Fort Worth, Texas, in April 2014. Hide Caption 5 of 13 Photos: Racer Tony Stewart Stewart makes a pit stop during the Daytona 500 in February 2014. Hide Caption 6 of 13 Photos: Racer Tony Stewart Driver Ryan Newman talks with Stewart in September 2013. Stewart broke his leg a month earlier during a race in Oskaloosa, Iowa. Hide Caption 7 of 13 Photos: Racer Tony Stewart Personnel prepare to load Stewart into an ambulance after his wreck in Oskaloosa in August 2013. Hide Caption 8 of 13 Photos: Racer Tony Stewart Stewart shakes hands with a member of the military at the Indianapolis Motor Speedway in July 2013. Hide Caption 9 of 13 Photos: Racer Tony Stewart Stewart sits in his car during a practice in July 2013. Hide Caption 10 of 13 Photos: Racer Tony Stewart Stewart celebrates with a burnout after winning a race in Dover, Delaware, in June 2013. Hide Caption 11 of 13 Photos: Racer Tony Stewart Stewart, in car No. 14, spins out after a wreck in Richmond, Virginia, in April 2013. Hide Caption 12 of 13 Photos: Racer Tony Stewart Stewart poses after winning a race in Daytona in February 2013. Hide Caption 13 of 13

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On Saturday night, Ward's sprint car hit the outside wall during lap 14 of a 25-lap race, Povero said.

A video of the incident shows two cars coming out of a turn with Stewart's No. 14 car sliding up the track toward Ward's No. 13 car. The two cars get close and appear to make contact before Ward's car hits the wall and spins out. Another car narrowly avoids hitting the 13 car as its sits on the track facing the wrong direction.

Ward gets out of his crashed car, walking on the track toward the racecars, which had slowed for a yellow flag. Ward points a finger and appears to be yelling. One car swerves to avoid Ward on the half-mile dirt track.

Stewart's car passes close to Ward, and it appears that its right rear tire hits him.

An ambulance took Ward to a hospital, but he died before it arrived, Povero said.

"Stewart has fully cooperated" with an investigation, Povero said. "He acknowledges the collision with the driver." It appeared to be an on-track incident, Povero said.

Ward, from Port Leyden, New York, was in his fifth season in the Empire Super Sprints series. He began racing when he was 4, running go-kart events.

Stewart's spokesman said officials are trying to sort out the details.

"A tragic accident took place last night during a sprint car race in which Tony Stewart was participating," Mike Arning said. "Tony was unhurt, but a fellow competitor lost his life. Our thoughts and prayers go out to his family and friends."

A competitor that runs the car that swerved around Ward expressed sympathy.

"Our deepest condolences go to the entire Ward Family. We are one huge ESS family, you will be truly missed bud! #RIP13," Hebing Racing tweeted.

Stewart is a three-time champion in NASCAR's top division and won a sprint car championship in 1995.

Tony Stewart did not drive Sunday in a NASCAR Sprint Cup race at Watkins Glen International race track.

"Our thoughts and prayers go out to the family, friends, and fellow competitors of Kevin Ward Jr.," NASCAR said in a written statement Sunday. "We support Tony Stewart's decision to miss today's race, and we will continue to respect the process and timeline of the local authorities and will continue to monitor this situation moving forward."

Stewart also owns a dirt race track in New Weston, Ohio, and has frequently raced sprint cars during the NASCAR season. He broke a leg last year in a crash that ended his racing season. He has raced the full NASCAR season this year but only returned to sprint cars in July.