Thirty independent investigators from the Organization for the Security and Co-operation in Europe (OSCE) have arrived at the crash site of Malaysia Airlines Flight 17, believed to have been shot down by a surface-to-air missile over disputed territory in Ukraine.

The OSCE observers arrived with the blessing of the pro-Russian gangs that currently control the area of Donetsk, the group said in a statement. According to the OSCE, the separatists committed to allowing “safe access and security guarantees to the national investigation commission” to international investigators as well as local authorities, who will be allowed into the area to assist in cleanup. The rebels also vowed to “cooperate with the relevant authorities of Ukraine on all practical questions arising in the course of the recovery and investigation works.”

The monitors will be working out of the village of Grabovo, which is nearest to the crash site, according to the BBC. While the group aims to assist in finding human remains and clearing the site, it is impossible to know what sort of valuable information they will acquire from looking at the site, particularly given that it is unknown how many of the jet’s black boxes are in the possession of separatist rebels and what the rebels have done with those they have allegedly found.

The mission is expected to face all manner of difficulties in finding useful evidence. Matt Robinson, a crash reconstruction expert that has worked in war zones, tells NBC that such an investigation is a “huge challenge,” as the separatists are expected to carefully monitor investigators. The presence of Ukrainian officials, even local officials and not any sent in from Kiev, could fuel a competition between the two groups to show who is most in charge of the investigation. Robinson adds that a third unknowable factor is the potential presence of looters who come to crash sites looking to find any valuables.

While only the fact that the plane was shot down by a surface-to-air missile has been confirmed by U.S. intelligence, evidence points to the possibility of pro-Russian groups in Donetsk accidentally shooting the plane out of the sky. Months ago, NATO warned that it believed that Russia was training separatist gangs in eastern Ukraine on how to use sophisticated anti-aircraft equipment, and it is believed that such missiles were in the rebels’ possession. Intercepted phone calls translated by the Kyiv Post also point to separatists discussing the missile attack and what appear to be the unintended consequences of killing hundreds of unrelated civilians.