Transcript for Was There a Russian Hand in the Malaysia Airlines Tragedy?
President Obama, today, called the shooting down of Malaysia airlines flight 17 an unspeakable outrage. So, who are these separatists believed responsible for the loss of so many lives? New evidence is shedding light on the men behind one of the worst attacks in airliner history. And how they pulled it off. Here's ABC's chief investigative correspondent, Brian Ross. Reporter: Until they were accused of the atrocity that took 298 lives, the pro-russian rebels in Ukraine, had portrayed themselves as heros. They put up movie-like billboards, promoting their cause. And photographers and reporters were invited to this recent wedding of one of the wounded fighters, whose bride also wore a gun over her shoulder. And among the honored guests was their top military commander, a Russian, not a Ukrainian, who uses the name, igor strelkov, which means igor the rifleman. He has a long-standing relationship with the Russian intelligence services. With ties to the Putin regime in Moscow. Reporter: Strelkov says he is fighting so people in Ukraine who want to be Russian or independent can do so. But under strelkov's command, the separatist militia fighting in Ukraine has become known as a ruthless gang of egotistical thugs, well-armed and trained by the Russians, according to U.S. Intelligence officials. That's a core of the Ukrainian separatist movements are people who are not Ukrainian. They are Russians. They are soldiers of fortune. Rambo types. They like to fight. They like to kill. And they are usually rewarded for that, very well, by the Russian government. Reporter: Friday, as strelkov's rebels patrolled the crash site, they denied reports they were responsible for shooting down the Malaysian air jetliner. Here is what we know. Reporter: But the evidence gathered by the U.S. Continues to mount against them. Presented in its fullest form Friday by the U.S. Ambassador to the united nations, Samantha power. Separatists were spotted hours before the incident, with an sa-11 system at a location close to the site where the plane came down. Reporter: At the same time today, Ukraine released this footage. It says shows the actual russian-made sa-11 missile launcher that brought down the plane, near the scene, right before the strike. U.s. Officials believe the rebels shot down a cargo plane earlier in the week. But hit the wrong plane on Thursday because they did not fully understand how to use the sa-11 system. They made a mistake. And shot down what they thought was another Ukrainian cargo plane. Reporter: According to phone calls intercepted by Ukraine, a separatist militant first reported the plane had been shot down. Are there any weapons, the person asks. Nothing at all. Civilian belongings. Medical scraps. Towels. Toilet paper. Told that the wreckage made clear it was a Malaysian airliner. Another person answers -- well, then it was bringing spies. Why were they flying? There's a war going on. In fact, that's a question many are asking now in the wake of the tragic incident Thursday. At the time, passenger aircraft were permitted to fly over the combat zone in Ukraine, as long as they were above 32,000 feet. Among the dozens of airlines that overflew the area in the last week, united airlines, lufthansa, virgin, klm and Singapore airlines. Even after a number of military aircraft had been shot down by the rebels. All those airlines have stopped flying over the area now. Everyone associated with commercial aviation is taking a look, not just at the Ukraine. But at Iraq, Afghanistan, any area where there's hostility and saying, is our idea that we can fly above hostilities and be safe -- is that accurate? Reporter: Aviation experts say, if no-fly Zones were declared in all of the world's hot spots, air traffic into and through the middle east and southwest Asia would become very difficult. As all of these airlines trying to reshuffle their routes and try to avoid, you know, areas of conflict, that may very well add distance to flights, which means burning more fuel, which means more costs. Reporter: And other than air force one, few passenger jets are equipped with anti-missile systems. Aircraft are vulnerable to attack within the plane, but also from the ground. Reporter: Our report on "Nightline" ten years ago, featured a new system that could detect and deflect some less-sophisticated missiles. But the cost then was calculated at more than $1 million a plane to install. And even at that price, it was hardly fool-proof. So, commercial aircraft today essentially fly unarmed, naked, against a threat that was considered highly unlikely until this week. Officials in the U.S. And Ukraine say, the best defense is to bring to justice those responsible for shooting down Malaysia air flight 17. I would say that this is very, very, very outrageous crime. And all those who commit that crime should be brought to justice. Reporter: But that may be difficult. There are already indications a cover-up could be under way. International investigators were kept from the accident scene. And today, Ukraine officials released this video, showing what they said was a surface-to-air missile system, in the same area as the crash, being returned to Russia, with only two of its four missiles still onboard. And no one seems sure, tonight, about the whereabouts of the jet's black box, which the U.S. Has demanded remain at the site. But the rebels say they will send to Moscow. Ukraine officials say the cover-up is already under way. So many wanting answers.
This transcript has been automatically generated and may not be 100% accurate.