A flight voice recorder, or "black box," sits in a cooler of water waiting to be analyzed by the Canadian Transportation Safety Board. REUTERS/JIM YOUNG

Word that the “black box” flight recorder for Malaysia Airlines Flight MH17 had fallen into the hands of the very pro-Russian rebels suspected of shooting the plane down has, not surprisingly, stoked international concern that key evidence about the tragedy will be manipulated, or even lost forever.

Armed Kremlin-backed separatists took control of the Ukraine crash site immediately after the plane went down near the Russian border Thursday, killing all 298 passengers and crew members aboard. The Boeing 777 jet was flying from Amsterdam to Kuala Lumpur when it suddenly went down in Torez, Ukraine, a disputed region largely under the control of rebel groups with ties to the Russian military. Exactly what caused the crash remains unconfirmed, yet initial witness accounts claiming a missile took down the jet have been echoed by U.S. President Barack Obama.

“This was a global tragedy,” he said at a White House press conference Friday. “An Asian airliner was destroyed in European skies filled with citizens from many countries, so there has to be a credible international investigation into what happened.”

Much of the credibility of that investigation could rest on what is done with the black boxes, oner of which the rebels have handed over to Moscow, according to the Interfax-Ukraine news agency. The vital piece of equipment includes a cockpit voice recorder (CVR) and a flight data recorder (FDR), which tracks the time, altitude, airspeed and direction the plane traveled, among dozens of other small details, including minor wing-flap movements and fuel levels. “Black box” is simply a shorthand term for the two pieces, which are stored separately in the plane and in fact painted bright orange to facilitate easy recovery.

Black boxes were widely adopted in airlines beginning in the 1960s, with most devices now capable of carrying no less than 25 hours of flight data and able to sustain a fire burning at 2,030 degrees Fahrenheit for an hour and 500 degrees Fahrenheit heat for 10 hours, according to National Geographic.

Of all the plane crashes in the past 50 years, there are only 17 instances when either the CVR, FDR or both were lost or rendered unusable. In eight of those 17 cases, the cause of the crash was determined, while questions remain in the nine other cases.

Malaysia Airlines Flight MH370 is the most recent addition to that list, as the plane, which disappeared March 8, has not been recovered. And 9/11 investigators never recovered the black boxes from the two flights that crashed into the World Trade Center on September 11, 2001.

Coincidentally, the black box was also never recovered from the crash of Siberia Airlines Flight 1812, which was accidentally shot down by the Ukrainian military over the Black Sea on October 4, 2001. The flight was traveling from Tel Aviv, Israel to Novosibirsk, Russia, with many of the 66 passengers and 12 crew members (none of whom survived) traveling to visit relatives. With the disaster coming so close to the 9/11 attacks, Russian authorities initially suspected that Chechen terrorists were responsible, until Ukrainian officials confessed that the cause was “an accidental hit from an S-200 rocket fired during exercises.”

Scott Hamilton, director of the aviation consultancy firm Leeham Co., told NPR News that in many of those 17 cases the black box was never found because it ended up at an unreachable ocean depth.

It is extremely rare for a black box to be destroyed. Black boxes have traditionally outperformed their design,” he said. “It would take a concentrated [hit] beyond its design strength, or an impact so high that it would be beyond what it could withstand.”

Ukraine has recognized the need to recover the black box, contacting the Paris office of the International Civil Aviation Organization Friday and asking for help with the accident investigation.

Kommersant FM, a Russian radio station, reported that in the case of MH17 the black box had been recovered and was en route to Moscow “for investigation” purposes. This, when combined with the growing narrative that the Russian government, in the words of Connecticut’s Democratic Senator Chris Murphy, has “blood on its hands,” conjures images of shadowy Cold War tactics. Yet it’s important to note that an official at Ukraine foreign ministry said the rebel forces have allowed Ukrainian government emergency workers to visit the site.

“Ukrainian experts are working in close cooperation with international specialists,” spokesman Andrii Sybiga told reporters, as quoted by the New York Times. He did add, however, that the “situation on the [site] of the catastrophe is dynamic. Our efforts to arrange the procedures in a proper way are being impeded by the terrorists.”