Malaysia Airlines crash site is "contaminated": Expert

Within minutes of Malaysia Airlines Flight 17 crashing to the ground in eastern Ukraine Thursday, people began arriving at the scene. Reporters, area residents, and Russian separatists surveyed the scene, took photos and videos, and, quite possibly, interfered with investigators' ability to properly assess the crash site.

"It's a contaminated site," said CBS News Transportation and Safety Analyst Mark Rosenker, who is a former chairman of the National Transportation Safety Board. "It's absolutely horrible. Parts could be missing."

Rosenker said it is critical to first have local authorities securing a crash site until crash investigators arrive, something that apparently wasn't done on Thursday. The most important piece of evidence investigators need is the plane's black box, which records conversations in the cockpit and the flight data, but investigators will also need critical parts of the aircraft including the nose, tail and wings.

Those parts will be necessary to determine where exactly the plane was struck by the missile that brought it down, and any explosive residue left on the pieces will provide evidence about what type of missile it was.

Furthermore, the bodies of the passengers, which will likely be recovered by local authorities, need to be examined to determine how exactly they died.

The black box is the most critical element to recover, Rosenker said. Although it is built to withstand heat and force, once the box is opened it becomes "a very delicate instrument that needs to be carefully handled through expert analysis."

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"You run a risk of tampering, you run a risk of somebody attempting to open it who doesn't know what he's doing - you could destroy the data," he warned. "Neither the Ukrainians nor the Malaysians are capable of doing a sophisticated investigation which is required to come to a transparent probable cause. They will need all of the technical help they can get in order to do this properly and to have a credible investigation that gives you a credible determination result."

There are reports that Russian separatists in Eastern Ukraine claimed to have picked up the black box, and they could hand it over to Russian authorities. While Russia has the capability of reading the box, Rosenker said, it will need to be done in the presence of international observers and experts to ensure a credible result.

"Clearly the smartest thing that could happen at this time is that the Ukrainians would invite, as a protocol, those professional investigative bodies in to be part of that investigation and be as transparent as you possibly can so that the truth will come out," Rosenker said. That includes the U.S. government and the National Transportation Safety Board, the British manufacturers who make the plane's engines, and the Malaysian government. Other countries whose citizens were on board may wish to observe as well.

Both President Obama and Vice President Biden said Thursday that Ukrainian President Petro Poroshenko had agreed to accept U.S. help. Biden said the experts "will be on their way rapidly to see if we can get to the bottom of this."