National Transportation Safety Board member Tom Chapman said during a news conference on Tuesday that the discovery of tail parts confirmed the plane was breaking apart before it hit the ground.
Chapman said the tail's elevator was broken into three parts, and without that intact, the pilot would not have been able to pull the Learjet out of its nose dive.
"The function of the elevator is to control the pitch up and down," he said on Monday.
"At those speeds I don't know that it would've been effective even if it had still been attached to the aircraft, but knowing that it was lost is a very important piece of evidence in terms of pointing us towards other things to investigate."
Chapman acknowledged that parts of the jet started to break off before it struck the ground and said weather would also be a key focus of the investigation..
The co-pilot, Nathalia Gadelha Filgueiras, told air traffic controllers minutes before the crash that ice was accumulating on the plane and that severe turbulence had thrown it up and down by more than 700 feet.
"We're going to die!" she said with a scream before the jet hit the ground and erupted in a fireball.
Family and friends of one of the pilots have been posting online about the longtime aviator, husband and father from the Philadelphia suburbs.
Jeff Gregory, 55, was one of two crew members in the cockpit of the Bahamas-bound Learjet 60 as it encountered bad weather and slammed into the ground on Sunday afternoon in Greenacres, southwest of West Palm Beach.
As the plane plunged, a man's voice could be heard reciting the Lord's Prayer in the background of the co-pilot's final radio transmissions to air traffic control. Friends are convinced it was Gregory, a devout Christian.
The Learjet hit the ground with enough force to create a crater before bursting into flames. The impact scattered plane fragments over a large area.
Images of the moment just before the aircraft made impact appear to show the elevator - a horizontal stabiliser - missing from the tail. About 600 nearby residents remain displaced, but only one injury was reported on the ground.
The plane took off from Austin, Texas. The victims included technology entrepreneur Adam Robinson, his wife, Helen Sharp, and their two young children, relatives said.
Filgueiras' stepfather, Thiago Corteleti, told the New York Post that she texted her boyfriend about 10 minutes before the crash, telling him: "I've got turbulence, I've got ice."
In the last two minutes of the flight, Filgueiras shifted from calmly communicating with air traffic controllers to calling out terrifying updates as the plane plummeted.
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