Investigators were hampered by ice on Saturday as they searched for bodies and clues in the wreckage of a commuter plane that slammed into a house in western New York state, killing 50 people.
"It is a slow process but we are making progress," said Steve Chealander of the National Transportation Safety Board.
Despite delays caused by frozen water from fire hoses and the mingling of debris from the plane and house, he told a news conference the NTSB hoped to wrap up the investigation in the Buffalo suburb of Clarence Center by Wednesday.
"The medical examiner believes that three to four days are going to be required to recover the victims of this crash," he said. "They've already pulled some of the folks out of there."
Speculation has focused on the wintry weather as the cause of Thursday night's crash, when the Dash 8 Q400 turboprop plane pitched wildly in its final approach before plunging to earth, killing all 49 people on board and one person in the house.
Two women in the house survived.
Chealander said it was too early to know whether ice was to blame. The mechanical systems seemed to be working normally, he said, but there would be more clarity when a team in Washington begins a detailed analysis of the flight recorders on Sunday.
The plane's crew reported snow and mist and commented on ice buildup on the windshield and front of the wings shortly before the crash, according to the cockpit voice recorder.
Flight 3407 to Buffalo from Newark, New Jersey, was operated by Colgan Air for Continental Airlines. Colgan is a unit of Pinnacle Airlines.
The plane's manufacturer, Canada's Bombardier Inc, said it was the first fatal crash of a Dash 8 Q400.
The delicate and gruesome task of recovering remains and evidence from the site about 10 km from the Buffalo airport was being handled by 100 to 150 NTSB investigators, FBI agents, coroners and volunteer firefighters.
Bodies were being taken to the Erie County medical examiner for identification.
"In some cases, we'll need to use DNA. In some cases, maybe we won't," Dr Anthony Billittier, Erie County's health commissioner, told the Buffalo News.
Search crews were being respectful and careful to ensure "the proper dignity is provided to the victims," said Laurie Bennett, special agent in charge of the Buffalo FBI office.
As the plane descended toward the airport with its landing gear down, its nose suddenly and violently moved up and down and its wings see-sawed, investigators said after initial reviews of the flight data and cockpit voice recorders.
Despite witness accounts that the plane nosedived into the house, Chealander said the wreckage was lying flat and the nose was pointed in the opposite direction of the runway.
The crash was the first deadly accident for US airlines since August 2006, when a similar number of people were killed when a Comair jet crashed on takeoff in Kentucky.
It was the third fatal accident since 2003 for Pinnacle and its Colgan unit, according to safety records. The two previous flights, which were not carrying passengers, resulted in the deaths of four crew members.
Thursday's disaster came less than a month after the successful crash landing of a US Airways jetliner on the Hudson River in New York City.
All 155 people on board survived when pilot Chesley ‘Sully’ Sullenberger brought the plane down safely on the river after it hit birds, taking out both engines.