Three days ago, a Malaysian passenger jet with more than 200 people on board vanished in the skies over Southeast Asia. On Monday, investigators appeared to be no closer to explaining how a large plane could seemingly disappear into thin air. A large-scale search involving boats and planes from a range of countries continues at sea. Relatives of the people on board keep up their painful wait for news. Officials have warned them to prepare for the worst. And theories abound about what may have taken place. Until clearer information comes to light, here’s a summary of what we know and what we don’t know about Malaysia Airlines Flight 370.