Investigators digging in to what happened to Malaysia Airlines Flight MH17 face enormous obstacles that go far beyond the obvious threat to their personal safety, as armed fighters and even looters swarm to the site, aviation experts say.
"Oh, my gosh. I've done a couple of investigations in combat zones, and it's a huge challenge," said Matt Robinson, a member of the International Society of Air Safety Investigators who's a crash reconstruction specialist with the investigative firm Robson Forensic of Pennsylvania.
"This is chaos here," Robinson added.
Aviation experts and government officials agreed that the top concern is the safety of the investigators.
"Our efforts are complicated by the presence of insurgents in the area," a duty officer for the Ukrainian State Emergency Service told NBC News. "The place is controlled by the militants — our people at the crash site are followed by armed men."
But there are also political, military and economic factors at play that could severely restrict how much time investigators could actually spend at the scene, Robinson said.
The site will attract Ukrainian security forces and rebels fighters alike eager to score political points by appearing to be in charge, he said. Pro-Russian separatists claimed to have recovered most of the jet's black boxes, The Associated Press reported early Friday.
And "an aircraft includes lots of valuable materials" — making the crash site a magnet for scavengers, scrappers and other "interlopers," he said. Off-duty coal miners were among those gathering evidence at the site early Friday.
"This needs to be quarantined," Robinson said. "People will actually abscond with pieces and parts of the aircraft."
Who'll Be in Charge?
Senior U.S. officials told NBC News they believed the aircraft was shot down by a surface-to-air missile. But it could be months or even years before an official determination could be nailed down. The first problem will be figuring out who's ultimately in charge of the international inquiry.
The flight went down in Ukraine, so under regulations of the U.N.'s International Civil Aviation Organization, it would have the lead role, but that assumes "everything is done according to the book," which is highly problematic, said Kenneth Button, director of the Center for Transportation, Policy, Operations and Logistics at George Mason University in Virginia.
"The other interests are purely subservient," Button told NBC News on Thursday. At the same time, "all airspace is sovereign," he said, so "any country can do exactly as it wants," and there's no international aviation court to sort out the competing interests.
As the country where the flight originated, the Netherlands could stake a claim. So could Malaysia, where the flight was headed. And Ukraine could invite other countries, such as the U.S., because the plane was manufactured by Boeing Corp.
"I'm afraid it's going to be a real mess," said Ross Aimer, a retired United Airlines pilot and chief executive of Aero Consulting Experts of Los Angeles.
Ukraine initially proposed that the investigation be led by the Ukraine State Commission, the ICAO and representatives of the Netherlands and Malaysia.
A senior Obama administration official told NBC News that a coordinated international investigation was imperative.
"There were people on the plane for several nations, and due to the ongoing conflict between Russia and Ukraine, we believe strongly that the international community needs to play a role in determining what happen here," the official said.
Greg Waldron, Asia editor for FlightGlobal magazine, told the BBC: “The plane has come down in contested territory so there has to be some concern. By rights the aircraft is owned by Malaysian so under international law Malaysia should have a key role in any investigation.
“If parts have been sent to Russia, as is reported, that it would be beyond standard operating procedure, certainly.”
Robinson said Malaysia's involvement would likely involve many of the same teams and experts who have been working for months on the disappearance of another Malaysia Airlines Flight MH370, which vanished March 8 on a flight from Kuala Lumpur to Beijing.
"That's their job," he said. "That's their expertise."
But in the long term, Aimer agreed with Robinson that physical safety was still the biggest barrier.
"You're in a war zone. That's going to be pretty tough," Aimer said. "If not invited, I certainly wouldn't go there ... I would say good luck to anyone who takes it on."
Jim Miklaszewski, Kristen Welker, Courtney Kube, Irina Tkachenko and Marc Smith of NBC News contributed to this report.