News photographer Bill Strothman and pilot Gary Pfitzner died Tuesday in the crash shortly after taking off from a helipad on a rooftop at Fisher Plaza.
An investigator said witnesses described hearing an "unusual noise" that indicated something was wrong when the aircraft took off.
"I heard it, it sounded like in the movies -- when it goes into slow motion, when you hear the ding, ding, ding ... and after that I heard it collapse. I heard it hit the ground, and that's when I looked up," witness Daniel Alejandro Gonzalez said.
“His noise pointed west, he banked right. He was basically sideways, he almost did a barrel roll. It hit and it instantly burst into flames, it instantly exploded," witness Chris McColgan said.
The National Transportation Safety Board and the Federal Aviation Administration are investigating the cause of the crash.