"This is just the beginning of this accident investigation," National Transportation Safety Board member Mark Rosekind told KOLO-TV, Reno, Saturday night. He said the investigation could take six to nine months.
Investigators Sunday were collecting more evidence at the crash site of the Reno National Championship Air Races, KOLO said.
"It's pretty clear that at low altitude and high speed, the aircraft went nose up, climbed briefly and then nose over quickly, that's why it impacted," Rosekind said.
Investigators said a piece of the plane may have come loose from its tail, causing it to crash into the crowd Friday.
"We're aware of that and in fact a component has been recovered in the area of where that was observed, but I think it's critical at this point to know that we have not identified the component. It will be examined so we don't even know what the component is or if it even came from this particular aircraft," Rosekind said.
Kelly was scheduled to pilot the same type of World War II era plane that was involved in the crash. However, Giffords' spokesman Mark Kimble said Kelly was not at the event when the crash occurred.
Giffords was shot in the head during a public appearance in Tucson Jan. 8. and is undergoing rehab in Houston.
2014: The Year in Music [PHOTOS]