Stewart also said he wanted Ward's family "to know that every day I'm thinking about them and praying for them" and that their suffering was "something I can't possibly imagine."
Stewart's comments came in a statement he read at a press conference at Atlanta Motor Speedway, where he is returning to NASCAR Sprint Cup racing this weekend after being in seclusion for three weeks following the Aug. 9 incident.
He took no questions from the media, mainly because the Ontario County (N.Y.) sheriff's office is still investigating the tragedy. "I need to respect the ongoing investigation process," he said.
Stewart, a three-time Cup champion, has not been charged with any wrongdoing in connection with the night-time incident at the Canandaigua Motorsports Park dirt track in upstate New York.
The Ontario County Office of Sheriff sent an email to media members Friday, saying, "The investigation into the death of Kevin A. Ward Jr., which occurred August 9, 2014, at the Canandaigua, New York Motorsports Park will continue for at least another two weeks. The Ontario County Office of Sheriff has reviewed this investigation, as it has been developed to date, with members of the District Attorney's Office. The Office of Sheriff will continue to apprise the District Attorney of information as it is developed. When the investigation is completed, the news media will be advised as to what action will be taken. The Ontario County Office of Sheriff thanks all media outlets for their patience and understanding as we continue to thoroughly investigate this tragic crash."
The incident began when Stewart and Ward were racing side by side and Ward's car crashed into the fence. Ward then got out of his car, walked on the track and appeared to be angrily gesturing toward Stewart when he was struck as Stewart's car circled back around.
The story and a graphic amateur video of the incident went viral and triggered a heated public debate about who might have been at fault.
Seated in front of a white backdrop devoid of the normal sponsor or speedway logos Friday, the 43-year-old Stewart said this was "one of the toughest tragedies I've ever had to deal with. This is something that will definitely affect my life forever."
Stewart said he stopped racing "out of respect for Kevin and his family and also to cope with the accident in my own way. It's given me the time to think about life and how easy it is to take it for granted."
But Stewart said he wanted to get back behind the wheel of his No. 14 Chevrolet because it would "help me get through this difficult time."