As the Russian government tries to determine what could have caused Metrojet Flight 9268 to break up in flight, some of the victims' bodies have arrived in St. Petersburg.
Russian forensic experts began trying to identify the remains of the passengers who were killed when an Airbus A321-200 crashed in Egypt on Saturday.
Reporting from Moscow, NPR's Corey Flintoff reports that Russian officials have yet to determine the cause of the crash. But the airline has said that the crash was unlikely to have been caused by human or technical error.
Corey filed this report for our Newscast unit:
"Investigators say all 224 people aboard the Metrojet airliner were killed when the plane crashed in Egypt's Sinai Peninsula.
"Officials asked family members to give DNA samples to help identify the dead. Russian officials at the crash scene say that the wreckage is spread over a wide area, indicating that the plane broke up in the air.
"Investigators are declining to speculate on the cause of the disaster.
"An Egyptian rebel group that's affiliated with the Islamic State has claimed responsibility for the crash. Russian and Egyptian officials dismissed that claim, saying the group didn't have the weaponry to hit a plane at a high altitude."
Meanwhile, the deputy director of Metrojet, Viktor Yung, told reporters that he did not believe the crash was caused by technical or human error.
According to the Russian-funded RT, Yung said the airline crew was incapacitated by the time the plane began plummeting.
Aleksandr Smirnov, who supervises the fleet of planes, told RT: "The only possible explanation is a mechanical force acting on the aircraft. There is no combination of system failures that could have broken the plane apart in the air."
RT adds: "The company gave assurances that the crashed Airbus had passed all necessary tests, including a check for metal fatigue in 2014, an inspection that must be done every six years."
The New York Times reports that, today, investigators are expected to begin analyzing the data on the black boxes that were recovered from the crash site on Saturday.
The paper adds that some experts believe an in-flight breakup could have been caused by pilot error:
"While Airbus aircraft are equipped with sophisticated software designed to help keep the plane flying within safe parameters, pilots must still maintain close attention to factors like speed, air temperature and altitude.
"A plane that was fully loaded with passengers and fuel, ascending too rapidly through the warm desert air, might have risked an aerodynamic stall, some analysts said. Depending on the speed of the descent, the aircraft might have been ripped apart as it tumbled toward the ground.
"Older aircraft in particular are vulnerable on very rare occasions to structural failure during ascent, as the passenger cabin is pressurized with more air inside than outside. Each time the cabin is pressurized, it is being slightly pushed outward like a balloon, and that puts stress on the fuselage."
Update at 2:04 p.m. ET. Don't Rule Out Islamic State:
Speaking at a Defense One summit, Director of National Intelligence James Clapper was asked if Islamic State militants could have brought down the Russian plane.
"It's unlikely but I wouldn't rule it out," he said. "We don't have any direct evidence of any terrorist involvement yet."