Sixteen other people were hurt in the crash.
"It was a scene of total chaos," said Bose, of nearby Odessa.
Shoemaker credited the training and courage of the veterans who jumped to help the injured. Her husband, Tommy, resuscitated one person and applied a tourniquet to a bleeding woman.
"They are trained for tragedy," Shoemaker said.
Spectators described their horror and helplessness as the train hurtled toward the flatbed tractor-trailer that was unable to move because of other floats in the parade.
"The train honked its horn, but the 18-wheeler could not go anywhere because of the other one being right in front of it," said Daniel Quinonez, who was waiting in his vehicle as the parade went by. "It was a horrible accident to watch happen right in front of me. I just saw the people on the semi-truck's trailer panic, and many started to jump off the trailer. But it was too late for many of them."
Marine Corps Chief Warrant Officer 3 Gary Stouffer, 37, and 47-year-old Army Sgt. Maj. Lawrence Boivin were pronounced dead at the scene, Midland police spokesman Ryan Stout said. Army Sgt. Joshua Michael, 34, and 43-year-old Army Sgt. Maj. William Lubbers died later at Midland Memorial Hospital.
Of those hurt, four are in stable condition and one is critical, Stout said. Ten others were treated and released from the hospital in Midland, about 320 miles west of Dallas.
At a prayer vigil Friday morning, Mayor Wes Parry's voice cracked as he described how he had met Boivin and his wife a day earlier.
"It's hard to believe today that he's not here anymore," Parry said.
Deborah Hersman, NTSB chairwoman, said Friday on NBC's "Today" show that the train was equipped with a forward-facing camera whose footage could help in the investigation. NTSB officials were heading to Midland on Friday to investigate the crash.