I tend to think that most of these murder victims did not make a conscious decision about jumping.
When you put your hand on a hot surface, you instantly pull it back.
You are right about the heat; I hope it's O.K. to post these excerpts; very lengthy article but important.
"The researchers are not trying to track individual identities, but to gauge the strength and speed of the fires. The number, location and time that people jumped could provide important clues to where the heat had grown particularly intense, according to Glenn Corbett, a professor of fire science at John Jay College of Criminal Justice in New York."
"Some commentators later remarked that those who had fallen had made a brave final decision to take control of how they would perish. Researchers say many people had no choice. Witness accounts suggest that some people were blown out. Others fell in the crush at the windows as they struggled for air. Still others simply recoiled, reflexively, from the intense heat."
"Temperatures in pockets of the buildings rose to more than 1,000 degrees Fahrenheit, or 538 Celsius, sufficient to weaken steel, according to researchers. The first people jumped or fell from the upper floors of the north tower just minutes after the impact of American Airlines Flight 11. The heat reached people on the upper floors long before the flames. Some of those trapped reported that the floor itself had grown so hot they had to stand on their desks, according to a fire official."
.
"The heat was absolutely phenomenal," said Guylene Proulx, who studies human behavior in fires for the National Research Council of Canada. "It was impossible to think you might survive. Why suffer a minute longer when it is so unbearable? It may have appeared to be the best thing to stop the pain, when the window is shattered and the opening is there."