Tony Stewart hit and killed driver Kevin Ward Jr., who walked toward Stewart's sprint car Saturday night after the two had an altercation at Canandaigua (N.Y.) Motorsports Park, according to authorities, witnesses and video of the tragedy. The three-time Cup champion was racing a sprint car in the Empire Super Sprints series at the half-mile dirt track in upstate New York, about an hour from Watkins Glen International, site of this weekend’s Cup race. UPDATE: Tony Stewart plans to race today at Watkins Glen The Ontario County (N.Y.) Sheriff’s Office confirmed in a news release that the victim, whom it did not name, was declared dead 45 minutes after the accident upon arrival at Thompson Hospital. "Mr. Stewart has cooperated with the investigation, which is ongoing," the release stated. Stewart was not arrested and the sheriff told reporters that the driver had returned to Watkins Glen. The case will be handled by the district attorney. Tyler Graves, a sprint-car racer and friend of Ward's, told Sporting News in a phone interview that he was sitting in the Turn 1 grandstands and saw everything that happened. "Tony pinched him into the frontstretch wall, a racing thing," Graves said. "The right rear tire went down, he spun on the exit of (Turn) 2. They threw the caution and everything was toned down. Kevin got out of his car. … He was throwing his arms up all over the place at Tony for most of the corner. "I know Tony could see him. I know how you can see out of these cars. When Tony got close to him, he hit the throttle. When you hit a throttle on a sprint car, the car sets sideways. It set sideways, the right rear tire hit Kevin, Kevin was sucked underneath and was stuck under it for a second or two and then it threw him about 50 yards." Rich Willis, who was at the track, said he didn’t see exactly what happened but his sister down in Turn 1 did. His description was similar to that of Graves and video of the tragedy showed Stewart's car hitting Ward. “People (who could see it better) said the guy got out of his car and was gesturing angrily at Tony Stewart when Tony Stewart came by during the next lap under yellow,” Willis said in a phone interview. “He approached him and evidently when he was driving by the guy standing on the track gesturing at him, he gunned his engine. “What happened was the back end kicked out and clipped the guy and the guy flew across the track.” Graves said it appeared to him that Stewart swerved before gunning the engine but he did not believe it was intentional. "You never mean to do something like that," Graves said. "Kevin was pissed and he let Tony know. And Tony was trying to give the message back that he wasn't happy either. He went over the line with it." Graves got emotional as he talked about Ward, whom he raced against last week in the Patriot Sprint Tour. In that race Graves' car broke, he got upside down and Ward hit him. "The first thing Kevin said to me (last week after the accident) was, 'I'm glad you're OK,'" Graves said. "He hit me full throttle. I've been friends with Kevin for the last several years. … He's a clean racer." The sheriff's department asked for any amateur video be sent to it for use during the investigation. It said the race was on lap 14 of a 25-lap event. "The driver of the car that spun, exited the race car and walked down the track onto the racing surface," the sheriff's news release states. "Two racecars traveling in tandem approached as the driver continued down the track, gesturing to the two approaching cars. "The first car swerved to avoid the driver out on the track. The second car, operated by Tony Stewart, struck the driver." The 43-year-old Stewart has 48 Cup wins in 542 career starts. Stewart, who missed the last 15 Cup races last year after breaking his leg in two places in a sprint-car crash, is winless and 19th in the standings this year. There was no immediate word whether Stewart-Haas Racing, co-owned by Stewart, would field Stewart’s car Sunday at Watkins Glen. With him released without being arrested, Stewart could race at The Glen, or the team could opt to put a different driver in the car or withdraw. Stewart is scheduled to start 13th . "A tragic accident took place last night during a sprint car race in which Tony Stewart was participating," an SHR spokesman said in a statement. "Tony was unhurt, but a fellow competitor lost his life. Our thoughts and prayers go out to his family and friends." Graves, who described himself as a huge Stewart fan until Saturday night, doesn't think Stewart should be racing. "Tony Stewart needs to be put in prison for life," Graves said.