Conflicting Theories Swirl in Metrojet Airliner Crash

— -- Conflicting theories behind a Russian plane crash in Egypt that killed 224 people continued to emerge today, as Russian authorities say they have entered the third part of the search, hoping to find clues to how the tragedy unfolded.

"Rescue teams have performed a search on eight square miles of the territory," said Alexey Smirnov, acting head of the Russian National Centre for Crisis Management of the Ministry of Emergency Situations. "Today at 7 a.m., emergency services units started the third stage of the operation, in which the search will expand to 12 square miles."

Two planes of the Emergency Situations Ministry delivered 140 bodies and more than 100 body parts to Russia, as well as personal belongings and documents, Smirnov added.

While Russian authorities said Monday the only explicable cause was a "mechanical impact on the aircraft," speculation that a bomb exploded or a missile hit the aircraft were addressed by Egyptian authorities. Egyptian President Abdul Fattah al-Sisi told the BBC that Saturday's crash was most likely the result of a technical fault, and not militants linked to the Islamic State, who claimed to have shot the plane down.

U.S. authorities are not part of the investigation, but Defense Department officials have told ABC News that flashes were picked up by satellite infrared sensors around the same time the plane was passing over the Sinai Peninsula, though these could have been unrelated to the aircraft in question.

Experts working at the scene of the Metrojet Airbus A321-20 crash found elements "that are not components of the crashed A321 airliner," Russian state-run news agency TASS reported today, quoting "informed sources in Cairo."

The analysis of the so-called black boxes has started, with authorities studying audio recordings on the Russian jet.

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