What's Next for the Flight MH 17 Investigation

— -- With investigators finally able to access the wreckage of Malaysia Airlines Flight MH 17, experts say they will now undertake the complicated search for answers in a debris field in a war zone in eastern Ukraine.

ABC News' aviation analyst and retired U.S. Air Force pilot John Nance said the wreckage has already been compromised by untrained people wandering through the debris.

"You recover the bodies, then you touch nothing else," Nance said, describing the normal course of investigations. "You preserve wreckage [but] in this case we've had people rummaging throughout the wreckage."

Nance said the investigation is unique because investigators are surrounded by the very people who are suspected of shooting the missile that brought down the plane.

The Ukrainian government has blamed the crash on Russian-backed separatists, who are now watching the site.

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On Friday, U.S. Ambassador to the United Nations Samantha Power said U.S. officials could not rule out the possibility that Russia helped launch the single surface-to-air missile that intelligence officials say brought down the plane.

The Ukrainian government today accused the milita members guarding the site of removing bodies and tampering with evidence. Rebels denied the report.

However, Nance said it's unlikely that an untrained person or group would know how to hide all the evidence of what happened aboard the doomed flight.

"There's so many pieces from which you can derive information, I think it's going to be difficult to do that unless they harass the investigators," Nance said.

Aside from dealing with potential inference with pro-Russian separatists, investigators are also examining a particularly long debris area stretching approximately 10 miles long. Nance said investigators would look for signs of how the plane broke up by examining where parts of the plane landed in the debris.

For example if the tail is at the beginning of the debris field, it shows the tail broke off first. That would also mean the flight data recorders or "black boxes" would have stopped working, since they are located in the tail.

Nance said investigators would also look for signs of implosion or explosion. An implosion would indicate a missile likely caused the crash, Nance said.

"There's not a flashing neon sign, but if you can see metal is splayed inward ... [it can be] an unmistakable sign of an explosion and maybe a missile," said Nance.

The Associated Press contributed to this report.