"I'm confident that we're going to figure this out," said Dennis Hogenson, with the National Safety Transportation Board, said at a news conference Wednesday afternoon.
Hogenson says they're looking at all possibilities, including what role, if any, construction cranes in the area played.
A crane operator was in radio contact with the pilot on a prior landing on the rooftop helipad, though there's no substantial evidence to link the cranes with the crash, Hogenson said.
Investigators also are poring over pilot, maintenance and company records, and they will recreate the crash scene to look for anomalies, he said. Wreckage from the helicopter has been moved to a secured hangar in Auburn, about 30 miles south of Seattle, where the team will lay out the pieces to determine what parts potentially are missing.
A large portion of the helicopter, which was built in 2003, was made of composite material that burned, so "a lot of those parts and pieces are simply gone," Hogenson said.
It may be months before federal investigators know what caused the KOMO-TV news chopper to hit the pavement and burst into flames Tuesday, setting three vehicles ablaze and spewing burning fuel down the street.
While a preliminary report could be released as early as this week, Hogenson said a final report could take up to a year.
The investigation team includes representatives from Airbus Helicopters, engine manufacturer Turbomeca, as well as the helicopter operator.
The helicopter wasn't equipped with a cockpit voice recorder or flight data recorder, which aren't required.
Witnesses reported hearing unusual noises coming from the aircraft as it lifted off from the helipad on top of Fisher Plaza after refueling, Hogenson said Tuesday. Witnesses also reported seeing the helicopter rotate before it crashed.
"It pitched sideways. It was off balance, and you could tell right away something wasn't right," said Bo Bain, an excavation foreman at a nearby construction project who watched the aircraft take off. "The helicopter was struggling to stay up. It spun around, hit the top of the tree and landed on the street."
Seconds later, "It was just a fireball. The whole thing burst into flames," he said.
Former KOMO photographer Bill Strothman (left) and pilot Gary Pfitzner (right)Mourners on Wednesday left flowers at the crash site to remember former KOMO veteran photographer Bill Strothman and pilot Gary Pfitzner. Both men were working for Helicopters Inc., which owned the Eurocopter AS350 helicopter. The aircraft was leased jointly by KOMO and KING-TV.
Mark Pfitzner told KOMO that his brother, Gary, put himself through flight school, loved to fly and "tried to do his best reporting for people."
News anchor and reporter Molly Shen remembered Strothman as "one of the best storytellers to have ever graced the halls of KOMO."
Richard Newman, 38, who suffered serious burns when the helicopter crashed on his car,