The report says the unplanned explosions were the result of a malfunction. The report explained that a firework failed to function as designed and the shell went off inside a mortar tube. That resulted in an explosion that triggered others.
The blasts sent debris from the fireworks, the racks holding them and the mortar tubes in all directions, injuring 28 spectators.
The report concluded the display was properly designed and set up. It also said Simi Valley police ruled out criminal activity or intent as a cause.