IndyCar said the results of the probe will be concluded within weeks, CNN reported.
The Automobile Competition Committee of the United States and the Federation Internationale de l'Automobile will assist in the investigation.
Two-time Indianapolis 500 winner Dan Wheldon died in the fiery pileup. He had been testing a safer IndyCar model for the 2012 season in the weeks before his death.
"The safety of our drivers, their crews, IndyCar staff, racetrack staff and spectators is always our paramount concern," the organization said in a statement, declining to comment further to the broadcaster on the probe.