Who fired on MH17?

Debris and human remains at the crash site of Malaysian Airlines flight MH17 close to Donetsk show the scope of the catastrophe: 298 people were killed on this flight that was scheduled to fly from Amsterdam to Kuala Lumpur. It becomes increasingly unlikely that the crash was simply an accident - many suspect the plane was shot down.

It's still unclear, however, who downed the plane. The conflict parties in the Ukraine crisis blame each other: Ukraine's army has accused pro-Russian separatists in eastern Ukraine of shooting down the plane, while the rebels have blamed Ukrainian forces.

Information from the United States suggests a missile attack brought the plane down. "This is one of the most heavily surveilled places on the planet, where they have satellites which are looking for missile launches because we're concerned about attacks from Russia," former CIA official Charles Duelfer told US broadcaster PBS.

Satellites picked up radar beams that could have been used to track the plane, according to US security experts. The satellites then noticed heat development, which could be attributed to a rocket launch.

'Not an accident'

That prompted US Vice President Joe Biden to infer that the incident was "not an accident" and to say the Malaysian aircraft had been "blown out of the sky."

"We urge all concerned - Russia, the pro-Russian separatists and Ukraine - to support an immediate cease-fire in order to ensure safe and unfettered access to the crash site for international investigators and in order to facilitate the recovery of remains," the White House said in a statement.

According to the Ukraine's secret service, there is evidence to pinpoint the perpetrators: It said it had listened in on phone conversations where pro-Russian rebels admitted to shooting down the Boeing 777-200. Just shortly after the crash, separatists apparently told Russian military forces that Cossack fighters had hit the plane.

It remains to be seen whether the phone conversations were genuine.

Rebel leader and "defense minister" of the self-proclaimed Donetsk People's Republic Igor Strelkov posted on a popular social network that his fighters shot down a Ukrainian cargo aircraft - the pictures are identical with pictures from the crash site of the Malaysian plane. The post was later removed from the network.

Putin says Ukraine is to blame

If the pro-Russian separatists indeed are to blame for shooting down the plane, it would also spell trouble for Russian President Vladimir Putin. The United States has repeatedly criticized Russia - especially since Moscow continues to supply arms to rebels.

However, US government officials stayed clear of pointing fingers. For his part, Putin said the Ukrainian government was responsible for the crash.

"This tragedy would not have happened if there were peace on this land, if the military actions had not been renewed in southeast Ukraine," Putin said, according to a Kremlin statement. "Certainly, the state over whose territory this occurred bears responsibility for this awful tragedy."

Ukrainian President Petro Poroshenko said the downing of the plane was a "terrorist act."

Did the separatists obtain such missiles?

The plane was apparently hit by a surface-to-air missile. The separatists have denied that they are able to hit an aircraft flying at 10,000 meters (33,000 feet).

Aviation expert Heinrich Großbongardt told DW that rebel and guerilla organizations never before had access to such type of weapons. They often had shoulder-fired anti-aircraft missiles of rather small caliber, but those could only reach an altitude of up to 4,000 meters, he told DW.

Other weapons systems are required to fire 10,000 meters into the sky. If it is proven that rebels downed the plane, one had to thoroughly check how they could get their hands on such a weapon, he added. The pro-Russian separatists had previously said they had obtained a mobile Russian anti-aircraft defense system Buk last week.

That, however, is a very sophisticated system and it's questionable whether they were able to learn how to operate Buk in such a short time. There are also reports that the Ukrainian military also has such weapons; it has denied firing any missiles.

The news of the plane crash came as a shock to the international community. German Foreign Minister Frank-Walter Steinmeier said he was horrified by the news from eastern Ukraine, "With hundreds of completely innocent people having died in this terrible way, words fail you."

He joined a number of other international politicians in calling for independent, international investigations into the downing of the plane and access to the site for emergency and security staff.

He was reluctant to talk about consequences at this point - he said consequences would depend on what had caused the crash.

In the meantime, separatists have said they allow investigators free access to the crash site.