It’s been four days since Malaysia Airlines Flight 17 was apparently shot down over a disputed region in Ukraine after taking off from Amsterdam en route to Kuala Lumpur.

Here’s what we know – and what we don’t know – since the tragedy occurred.

WE KNOW … MH17 was shot down using a surface-to-air missile system. This has been confirmed and reported in multiple media outlets. These heat-seeking missiles can be fired more than 12 miles into the air – that’s 60,000-70,000 feet high, easily able to take down a plane traveling at an altitude of 33,000 feet.

WE DON’T KNOW … who did it. Speculation has centered on pro-Russian separatists eager to return Ukraine to Russian control. The separatists have already shot down two Ukrainian military planes in the last three weeks. But Russia has blamed Ukraine loyalists for the downing of the plane. No matter who is responsible for this unspeakable tragedy, these surface-to-air missiles are complicated, sophisticated pieces of military hardware that are not only usually government property, but take extraordinary training to operate.

WE KNOW … 298 souls were on-board, including 15 crew members, from 11 different countries. This information was obtained from flight manifests.

WE DON’T KNOW … How many have been identified. Efforts to investigate the crash and the crash site have been hampered by the fact that the area is controlled by the Russian rebels, and there have been instances where investigators were not allowed into the crash site and debris field.

WE KNOW … Flight MH17 was basically flying over a war zone and that earlier this month the Federal Aviation Administration issued a NOTAM – Notice to Airmen – warning about flying over that region in Ukraine. But that NOTAM only goes to U.S. airlines. That route over Ukraine is not only heavily trafficked, it’s economical and timely.

WE DON’T KNOW … What difference 1,000 feet makes. Eurocontrol, the FAA-like agency responsible for coordinating European airspace, said Ukrainian authorities had closed airspace in the region below 32,000 feet last week. Why that entire route was not closed remains unclear but Flight MH17 was flying at 33,000 feet when it was shot down.

WE KNOW … Malaysia Airlines is in a world of trouble in terms of its viability as a carrier. The airline was already having financial difficulties for the past three years, and now has suffered two terrible tragedies in the span of less than five months, including the disappearance of Flight MH370 in March.

WE DON’T KNOW … If the government will approve a plan to back the airline financially or if another carrier will step in and merge with Malaysia Airlines.

WE KNOW … The aviation industry is taking matters into its own hands for the first time in a while. Emirates Airlines, a growing power, has called for an international airline summit to discuss safety concerns. Also, Karen Walker, editor-in-chief of the influential trade journal Air Transport World, noted that the tragedy came in the same week as the Farnborough Air Show in England.

She called for an industry boycott of air shows that also showcase  anti-aircraft weapons systems. "In truth, these air shows are also arms trade fairs. So I propose that airline executives join together and boycott air shows for as long as they are inclusive of both airliner makers and airliner destroyers,” she wrote on her blog.

WE DON’T KNOW … How effective any of this will be.