(CNN) The clues emerging so far about the final moments of Metrojet Flight 9268 don't paint a clear picture of what happened to the doomed passenger jet.

Was a midair heat flash that a U.S. satellite detected over the Sinai Peninsula when the flight went down a sign of an explosion aboard the plane? And if that was the case, why haven't investigators found signs of an explosive impact on the crash victims' bodies, as Russian state media reports? Could the plane's wreckage show that a past repair went awry?

There are a wide range of theories on what made the passenger jet plunge to the ground, killing all 224 people on board , but Russian officials say it's too soon to speculate on the cause.

Aviation experts agree, and officials have downplayed an apparent claim by Islamic militants that they brought down the Airbus A321-200, saying technical failure is the most likely reason for the crash.

Here's a look at the evidence investigators are looking at:

Radar

Flight 9268 was on its way from the Egyptian resort of Sharm el-Sheikh to St. Petersburg early Saturday when it dropped off radar about 23 minutes into the flight, Egyptian officials say.

Air traffic controllers apparently didn't receive any distress calls.

The website Flightradar24, which tracks aircraft around the world, said it had received data from the Russian plane suggesting sharp changes in altitude and a dramatic decrease in ground speed before the signal was lost.

Satellite data

A U.S. military satellite detected a midair heat flash from the Russian airliner before the plane crashed Saturday, a U.S. official told CNN.

Intelligence analysis has ruled out that the Russian commercial airplane was struck by a missile, but the new information suggests that there was a catastrophic in-flight event -- including possibly a bomb, though experts are considering other explanations, according to U.S. officials.

Analysts say heat flashes could be tied to a range of possibilities, including a bomb blast, a malfunctioning engine exploding or a structural problem causing a fire on the plane.

JUST WATCHED Did a bomb bring down Metrojet Flight 9268? Replay More Videos ... MUST WATCH Did a bomb bring down Metrojet Flight 9268? 02:05

Black boxes

Egyptian officials have said they are finishing fieldwork first, and then will go on to investigate the data in the black boxes . Experts started retrieving data from the recorders on Monday, Egypt's Civil Aviation Ministry said.

Photo of one of Flight 9268's "black boxes" released by Egypt's Ministry of Civil Aviation.

Russia's privately owned Interfax news agency quoted an unnamed source in Cairo as saying the plane's cockpit voice recorder had captured uncharacteristic sounds the moment before the flight disappeared.

It cited the source as saying that an "unexpected' and "nonstandard (emergency)" occurred "instantly," which was why the pilots failed to send an emergency or alarm signal.

A top Russian aviation official has said the plane broke apart in midair . Sounds in the black-box recording could help investigators determine what caused that to happen, said Peter Goelz, a CNN aviation analyst and former managing director of the U.S. National Transportation Safety Board.

"You can tell whether it is a high-order explosion, or a more low-order event, like a decompression and a tearing apart of the aircraft," he said.

The wreckage

The Egyptian committee investigating the Metrojet plane crash is expected to finish fieldwork on Tuesday evening, Egyptian Civil Aviation Minister Hossam Kamel said in a news statement Tuesday.

That's a sign that investigators will soon be closer to figuring out what happened, said Alan Diehl, a former accident investigator for the U.S. National Transportation Safety Board, the Federal Aviation Administration and the U.S. Air Force.

"This airplane went down in the desert ... and that makes it a lot easier to locate the critical pieces. But that is very quick, if they can do that and get the forensic wreckage evidence into the labs, that will be good news," he said.

Photos: Russian plane crashes in Egypt Photos: Russian plane crashes in Egypt The militant group ISIS published this image of what it claims is the bomb that brought down Metrojet Flight 9268 on Saturday, October 31. The photograph shows a soft-drink can and two components that appear to be a detonator and a switch. Flight 9268 crashed in Egypt's Sinai Peninsula en route to the Russian city of St. Petersburg. All 224 people on board were killed. Hide Caption 1 of 25 Photos: Russian plane crashes in Egypt The wreckage of Flight 9268 is seen in this image provided on Tuesday, November 3. Hide Caption 2 of 25 Photos: Russian plane crashes in Egypt People visit a makeshift memorial at the airport in St. Petersburg on November 3. Hide Caption 3 of 25 Photos: Russian plane crashes in Egypt Trucks in St. Petersburg carry victims' bodies on Monday, November 2. Hide Caption 4 of 25 Photos: Russian plane crashes in Egypt Russian emergency personnel collect personal belongings of victims at the crash site in Hassana, Egypt, on November 2. Hide Caption 5 of 25 Photos: Russian plane crashes in Egypt Egyptian military personnel stand near the tail of the jet in Hassana on Sunday, November 1. Hide Caption 6 of 25 Photos: Russian plane crashes in Egypt A piece of the engine sits on the ground at the crash site on November 1. Hide Caption 7 of 25 Photos: Russian plane crashes in Egypt Egyptian army soldiers guard the luggage and other belongings of passengers piled up at the site of the crash on November 1. Hide Caption 8 of 25 Photos: Russian plane crashes in Egypt Debris belonging to the Russian airliner is shown at the site of the crash on November 1. Hide Caption 9 of 25 Photos: Russian plane crashes in Egypt More debris is shown on November 1. The crash site is in a remote area of a region plagued by a violent Islamic insurgency. Hide Caption 10 of 25 Photos: Russian plane crashes in Egypt Debris from the airliner is seen on November 1. Hide Caption 11 of 25 Photos: Russian plane crashes in Egypt Debris at the crash site on November 1. Hide Caption 12 of 25 Photos: Russian plane crashes in Egypt Candles, toys, flowers and portraits are left at Pulkovo International Airport outside St. Petersburg on November 1. Hide Caption 13 of 25 Photos: Russian plane crashes in Egypt People place flowers and messages in front of the Russian Embassy in Cairo on November 1. Hide Caption 14 of 25 Photos: Russian plane crashes in Egypt Egyptian paramedics load the bodies of victims into a military plane at a military air base by the Suez Canal on Saturday, October 31. Hide Caption 15 of 25 Photos: Russian plane crashes in Egypt Egyptian Prime Minister Sherif Ismail, third from right, visits the site of the plane crash with military and government officials on October 31. Hide Caption 16 of 25 Photos: Russian plane crashes in Egypt Ismail, center, and other officials visit the site of the plane crash on October 31. Hide Caption 17 of 25 Photos: Russian plane crashes in Egypt An item of clothing lies at the site where the plane crashed on October 31. Hide Caption 18 of 25 Photos: Russian plane crashes in Egypt The tail of the jet sits in a field on October 31. Hide Caption 19 of 25 Photos: Russian plane crashes in Egypt Villagers watch an ambulance as it drives to unload bodies on October 31. Hide Caption 20 of 25 Photos: Russian plane crashes in Egypt People light candles and leave flowers at the Russian Embassy in Kiev, Ukraine, on October 31. Hide Caption 21 of 25 Photos: Russian plane crashes in Egypt A relative reacts to news at Pulkovo International Airport on October 31. Hide Caption 22 of 25 Photos: Russian plane crashes in Egypt Employees with the Russian Ministry for Emergency Situations wait in Moscow for their flight to Egypt on October 31. Hide Caption 23 of 25 Photos: Russian plane crashes in Egypt Journalists and spectators wait for ambulances to arrive at the Zeinhom morgue in Cairo on October 31. Hide Caption 24 of 25 Photos: Russian plane crashes in Egypt An Egyptian soldier prays as emergency workers prepare to unload bodies of victims at a military airport north of Suez, Egypt, on October 31. Hide Caption 25 of 25

State broadcaster Russia 24 reported that the aircraft's tail was found about 5 kilometers (3 miles) away from the rest of the plane wreckage. It did not show any signs of burning from a fire, the state broadcaster said.

Russian state media has reported that so far, investigators haven't found any traces of explosive devices in the debris.

Explosives expert Chris Owen, from Alford Technologies, told CNN that if swabs had been taken from plane debris quickly -- while the wreckage was dry -- it could be possible to identify any explosive residue in a lab.

"However, there would probably be quicker and more obvious evidence from the type of damage sustained by bits and pieces around the bomb," he said. "Surfaces in the vicinity of any explosion would be expected to be bent, perforated, petaled, spalled, sheared, frayed, charred (especially fibers), melded by impact, and otherwise characteristically damaged."

Owen said it would be hard to rule out a bomb blast just because evidence of one had not been discovered. "If a bomb is ruled out, it will likely be because another cause has been found," he said.

The plane's maintenance history

According to the Aviation Safety Network , which tracks aircraft incidents, the same plane's tail struck a runway while landing in Cairo in 2001 and required repair. At the time, the aircraft was registered to the Lebanese carrier Middle East Airlines, registration records show.

Kogalymavia's Andrei Averyanov said the plane had been damaged in 2001, but had most recently been thoroughly checked for cracks in 2013. Not enough time had passed for major cracks to develop to a critical size since then, he said.

CNN aviation analyst Mary Schiavo, former inspector general for the U.S. Department of Transportation, said she once worked on a crash where a tail strike that had not been repaired well brought down a plane almost two decades later.

Reports that the Metrojet Flight 9268's tail was found miles away from the other plane wreckage, she said, indicate something could have gone wrong with the repair work after the tail strike.

"To me, it says (the tail) exited the plane before the explosive event and before the fire engulfed the plane. ... A bad repair is like a ticking time bomb, because once it's on the plane, it stays with the plane forever," she said.

The A321-200 was built in 1997, and the airline company Kogalymavia, which flies under the name Metrojet , had been operating it since 2012, Airbus said. The aircraft had clocked around 56,000 flight hours over the course of nearly 21,000 flights, the plane maker said.

So far, officials have said all its inspections were in order.

Metrojet official Alexander Smirnov said the airline had ruled out technical problems and human error. Protection systems on the plane would have prevented it from crashing, he said, even if there were major errors in the pilot's control equipment. But authorities have said it's too soon to rule out any possible cause for the crash.

JUST WATCHED Report: Russian plane's condition concerned co-pilot Replay More Videos ... MUST WATCH Report: Russian plane's condition concerned co-pilot 03:29

The victims

Most of the bodies retrieved at the crash site are intact, a medical source in Sinai told CNN on Monday, and showed no major burns.

On the bodies of victims recovered so far, investigators haven't found any sign of explosive impact, Russian state media reported Tuesday , citing unnamed sources.

Russia's state-run TASS news agency reported that Russian and Egyptian experts had not found any blast-related trauma during their preliminary examination of the bodies, citing a Russian source within the investigation.

That doesn't eliminate the possibility that an explosion occurred, said CNN safety analyst David Soucie, a former accident investigator for the Federal Aviation Administration.

"A blast would not have to be very large ... to rupture the hull of that aircraft," he said.

The security situation

Sinai has been a battleground between ISIS-affiliated militants and Egyptian security forces in recent years. Hundreds have died in the fighting.

The militants appeared to claim responsibility for bringing down the Russian passenger jet in a statement posted online Saturday, but officials in Egypt and Russia have disputed that claim, saying there's no evidence to support it.

JUST WATCHED Egypt: Investigation will be honest, independent Replay More Videos ... MUST WATCH Egypt: Investigation will be honest, independent 03:50

Egypt's Interior Ministry said it wasn't stepping up security in Sharm El-Sheikh or at the resort city's airport "because there is no indication (the plane crash) was a terrorist operation."