The crash site of the Malaysia Airlines flight in eastern Ukraine holds many important clues about what happened to the plane. But that site is under the control of pro-Russian separatists who are suspected of involvement in shooting the plane down.
The rebel fighters say they are giving access to investigators, including those from the Ukrainian government, though one Ukrainian official who visited the scene Friday said he was not given full access.
Here are some of the key questions on the investigation into Flight MH17:
The U.N.