Transcript for Investigating Downed Malaysia Airlines Jet
Today's disaster in the air was one of the deadliest ever. But if as the U.S. Government now believes, the Malaysian airline flight was hit by a missile, it wouldn't be the first time a commercial airliner was shot out of the sky. What do past incidents tell us about what may have happened here? Here's Jim Avila. A debris field stretching for miles, the fuselage from the frame to the human body, decimated. A few miles away, entire, in-tact chunks, still carrying the airline's color scheme. Body, still recognizable in a rez dreshl neighborhood. The voice recorder on board which tapes the conversations, are unlikely to have recorded more than an explosion. The captain and first officer would not have seen a speeding missile coming their way. And the passengers never knew what hit them. At 33,000 feet, you'll be possessed of only a couple seconds before you black out. Even if the stunning effect of whatever explosion of whatever occurred hadn't already knocked you out. On the ground, everywhere you turn, clues of what brought this plane down from 33,000 feet. When you see wreckage and people still strapped in their seats, along a path of five, ten miles, like we have here, it indicates the airplane most definitely split up at higher altitude, and dumped not only people out, but dumped the entire section of the fuselage, and that's indicative of an explosion. He says because so many of the pieces show no evidence of fire, that indicates an explosion from an outside source. Where it happened, points to a missile. This is a war zone and people are firing at each other. It is possible for somebody to mistake an airliner, even at 33,000 feet, for a hostile airplane. It's happened before, at least twice. In both cases, the civilians planes were somehow seen as threats to the country that shot them down. That was dead on. On July 3rd, 1988, an Iran yane airliner with 290 people on board from Tehran to dubai, when it was shot down over the persian gulf, by a missile fired from a U.S. Navy ship. The us had been exchanging gunfire and mistakenly took the air 330 airbus for an Iranian fighter jet. Five years before that, in September 1983, a Korean passenger plane, with 269 on board was shot down by a Russian fighter jet after it accidentally strayed into then soviet airspace. The soviet government first denied involvement. Let us now listen to the tapes. But at the U.N. Security council, audio tapes made it clear, it was a deliberate act. In both of those cases, there had been something else going on in the area the day before. In the Ukrainian case, something was shot down the day before. So it's possible that people on both sides of the border, Russia and Ukraine, were seeing it through the lens of the continuing activity that's been going on on that border and thinking, this was not a passenger plane, but thinking it was a military plane. In this case, denial is possible again. The ethnic Russian opposition controls the Ukrainian land where the plane crashed. And the rebels claimed to have already confiscated those crucial black boxes, vowing to send them to Russia, former ntsb director Tom houder tells us, the data inside them cannot be altered without detection. It's very easy to tell if somebody has tampered with that data. So I'm not overly concerned about that. The key now is to get that data to the authorities as quickly as possible. Get the specialists on hand and download the information. Perhaps of more concern is the integrity of the crash site itself. In a war zone, maintaining a crime scene is not always the first priority. That's a major concern. Any time you have an uncontrolled accident site, parts vanish. It's just the way it is. We don't want that to happen here. Obviously, if they start removing parts, they may remove parts that are critical to the investigation. They don't know what they have. So there needs to be some control over the site. Any part that walks off, if you will, may be the critical part to help understands what happened here. A ten-mile debris path, with clues, answers, and the victims that carry them, now all guarded by hostiles, perhaps even the people who shot them down. For "Nightline," I'm Jim Avila in Washington. FBI officials will now be heading to Ukraine to aid in the crash investigation.
This transcript has been automatically generated and may not be 100% accurate.