An autopsy of world champion Norwegian swimmer Alexander Dale Oen, who collapsed and died in Arizona this week at the age of 26, has found no conclusive cause of death, a newspaper in the state reported late on Wednesday.
Authorities suspected that Dale Oen, the world 100 meters breaststroke champion, suffered a heart attack on Monday at an altitude training camp in Flagstaff in northern Arizona.
The autopsy conducted on Tuesday found no evidence of how he died, the Arizona Republic newspaper reported.
"The initial autopsy revealed no anatomic cause of death and no trauma associated with the death," Barbara Worgess, a chief health officer for the Coconino County Public Health Services District, said in a statement reported by the newspaper.
The Health Services District was not immediately available for comment.
Investigators were running additional tests and consulting with a cardiovascular pathologist, the newspaper said.
Dale Oen was found lying partially in a bath tub at the training facility after a day of light training and a game of golf. His teammates broke into the bathroom after noticing he had spent a long time inside.
A team doctor and paramedics tried to revive him.
He became a national hero in Norway last year when he won the 100 meters breaststroke at the world championships in Shanghai just days after Norway had been rocked by the massacre of 77 people by a far-right fanatic.
Dale Oen was one of his country's best hopes for a medal at this year's summer Olympic Games in London.