(CNN) -- Several times a day, helicopters land and take off from the helipad above Seattle's Fisher Plaza.
But this time was different.
The sound -- what the lead investigator described as an "unusual noise" -- gave away Tuesday morning that something was amiss. What followed immediately afterward proved it, as a news helicopter tumbled to the ground and burst into flames, with those flames spreading to several parked cars in its path.
"I looked and the helicopter was almost immediately pitched sideways and off balance," construction worker Bo Bain told CNN affiliate KING. "And he kind of just nose-dove over the trees, and clipped the top of the trees and crashed just on the other side of the street there."
The two people aboard the helicopter died in the crash, and another person who'd been in one of the three vehicles that caught fire was critically burned, officials said.
The incident rattled a vibrant part of the Emerald City, falling a few feet from the Space Needle and near the Experience Music Project, Children's Museum and the Bill & Melinda Gates Foundation offices, a quarter-mile away.
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Why did what had started out as a routine takeoff turn into a disaster? Authorities offered little clarity just after the crash, but promised to find out.
"We want to understand what actually happened, so we can understand what we can do in the future to prevent this from happening," Mayor Ed Murray said.
Man leaves car 'in flames,' bleeding
The 2003 Eurocopter AS350 was owned and operated by Helicopters Inc., a company that specializes in providing news-gathering copters. While KING indicated on its website that it sometimes made use of the helicopter, it was being leased at the time by CNN affiliate KOMO.
The helicopter had just come from Covington, Washington, and was planning to head next to Renton, said Dennis Hogenson with the National Transportation Safety Board, which is leading the investigation.
"A witness described as the helicopter lifted off from the building and began to rotate counterclockwise and subsequently crashed," he said.
Daniel Alejandro Gonzalez told CNN affiliate KIRO that he had gone outside to smoke a cigarette when he heard the helicopter's engine turn over. "About 15, 20 seconds later, 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."
Within a couple of seconds, the scene was ablaze.
Video showed what was left of the helicopter immersed in flames, as well as a line of fire in the street that engulfed several vehicles.
One man emerged from a car that was ablaze, with "his shirt ... in flames, his head ... bleeding," Gonzales said.
"He walked about 20 feet and he collapsed."
The injured man -- in his late 30s -- was taken to Harborview Medical Center in critical condition, with burns over 50% of his body, fire department spokesman Kyle Moore said.
A hospital spokeswoman, Susan Gregg, said doctors at the level-one trauma center had sedated the man, put him on a ventilator and were administering fluids. They were still trying to determine the extent and severity of the burns, she added.
Gregg said the man may have helped reduce the severity of his injuries by rolling on the grass, extinguishing the flames.
Media mourn loss of their own
Bain described the next few minutes as "chaotic," with people abandoning their cars and one driver who "made a U-turn and got out of Dodge as quickly as possible." The area was already abuzz with commuters heading to work but few tourists, since the Space Needle was still more than two hours from its scheduled opening.
Still, while it could have been worse, the crash had a devastating effect -- especially among those who knew the victims.
Murray described KOMO workers as being "in a state of shock."
KOMO identified the victims as Bill Strothman, a retired KOMO photographer who was working as a freelancer, and Gary Pfitzner, the pilot.
Strothman had earned 14 Emmy Awards during his career; his son works as a photographer for the station.
"He was a guy who really knew how his pictures could tell a million words," KOMO news anchor Dan Lewis said of Strothman, who also worked for the helicopter leasing company that was operating the aircraft. "... He was such a gentleman, a true gentleman."
Pfitzner too was a familiar face at the station. "He always had a smile on his face," said anchor and reporter Molly Shen. "He loved what he did, loved to be able to fly and be up there above the city and see things from a perspective that most of us don't get to see."
Seattle's mayor, Murray, met Tuesday with Strothman's family, having known the father and son.
"It just brought it home in a very personal way," the mayor told reporters. "... It just reminds us both that we are public servants. And people put themselves at risk in your business."
'Just a part of the tail and burnt-out metal'
Arriving firefighters found lines of blazing fuel in the street and thick, black smoke covering the area, with "wreckage strewn across the lawn along with wreckage across the street," said Moore, the fire department spokesman.
The first responders' prompt and "pretty outstanding" actions, as Murray described them, helped prevent a horrific situation from becoming worse.
Ten tons of sand were dumped on the street to absorb the helicopter's fuel, with vacuum trucks later heading to clean up the site, said the mayor.
The Space Needle closed due to the crash, as did the city's monorail and parts of streets in the area.
The helicopter did not appear to any have struck any nearby buildings before its fiery end.
"What we have left is basically just a part of the tail and burnt-out metal from the main chassis of the helicopter," Moore said.
Soon after the crash, investigators were interviewing witnesses, assessing the scene and gathering the wreckage in order to literally piece together what happened at an off-site location.
Hogenson, from the NTSB, said that his agency would issue a preliminary report in about five days and a full report -- including the probable cause of the crash -- within a year.
The president of Helicopters Inc., Stephen Lieber, issued a statement offering his company's condolences.
"We mourn their loss and suffering and our thoughts and prayers are with them," he said. "We will cooperate fully and completely with the National Transportation Safety Board and provide to it whatever information it wants in order to assist it in its work in determining what happened."
CNN's Mary Kay Mallonee contributed to this report.
Flames now out, told by a witness one person on fire when crawled out of a cars. 1 responders working on that person pic.twitter.com/zHeFzV0qzJ— Kelly Koopmans (@KellyKOMO4) March 18, 2014
Chopper tail visible amid the smoke & car wreckage pic.twitter.com/uZ57DibreU— Kelly Koopmans (@KellyKOMO4) March 18, 2014
2 DOAs at helicopter crash scene near space needle. pic.twitter.com/JwhBs2nYUF— Seattle Fire Dept (@SeattleFire) March 18, 2014
Medics transporting an approx 37 yo male to HMC in critical condition self extricated from car pic.twitter.com/hhVAX0qmbs— Seattle Fire Dept (@SeattleFire) March 18, 2014
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