(CNN) -- Bodies, backpacks, passports and other piles of debris lay splayed across a miles-long area in the remote area in eastern Ukraine where Malaysia Airlines Flight 17 came down. The crash site is massive -- an international observer called it "one of the biggest -- or the biggest -- crime scenes in the world right now."
Concern is growing that the site has not been sealed off as it should have been and that vital evidence is being tampered with. Meanwhile, armed rebels have greeted international observers with hostility.
Experts say that this crash investigation is unprecedented due to the site's immense size and the lack of access given to investigators.
With so many questions over what happened to MH17 unanswered, experts say it is crucial that the scene is protected. What should be being done on the ground?
How should a crash site be secured?
Keeping the crash site sterile is one of the most important steps that authorities take during the investigation, David Deas, the former spokesman for the U.K. Department of Transport, told CNN's Hala Gorani.
"It would be sealed off by security forces or law enforcement," Deas said.
After the site is secured, analyzing and removing the debris is an arduous process.
The investigation "will take hundreds of people several months," Tom Fuentes, a former assistant director at the FBI, told CNN's "New Day Saturday."
"They will need a convoy of trucks for the victims. They'll need a convoy of flatbed trucks, cranes to remove the debris. They'll need a location to take the debris to where it can be reassembled, examined and determine what exactly happened to the aircraft."
Why is this important and what will forensics experts look for at a crash site?
Although investigators need to survey the crash site to figure out what happened, the first order of business is to collect the victims' remains, according to Fuentes.
"Forget about the blame," Fuentes said. "You want to recover your victims, recover the remains, reunite them with their families. That's first and foremost."
Investigators also say that the proving who and what was responsible for the crash lies among the wreckage.
Seemingly minute details, like the direction in which debris fell, can provide information as to what took down the plane -- that's why it's so important to make sure the site is not tampered with.
"The only way that (culpability) is going to be truly determined is by the hard, physical evidence to prove that something did hit the aircraft," David Soucie, a former accident investigator, told "New Day."
Soucie says that evidence from the crash site can help investigators prove whether something hit the plane, what direction a missile might have come from and how far away the projectile was when it was launched.
In addition, the wreckage itself can create hazardous conditions for nearby populations, according to the National Transportation Safety Board.
And the airline industry can also use the information about what exactly took down the Boeing 777 when they construct newer planes.
"Lessons can be learned for the future construction of aircraft," Deas said. Investigators "want to know why it happened, but they also want to learn lessons from it."
What should happen to the bodies of victims?
As of yesterday, the remains of the victims had not neither been moved nor tampered with, a spokesman for the Organization for Security and Co-Operation in Europe told CNN's Christian Amanpour.
The bodies still have not been removed, more than two days after the incident, spokesman Michael Bociurkiw said from the crash site. Observers on the ground say they are starting to decompose and bloat. And with the summer heat, there are notable health implications if the bodies remain outside for too long,
The remains need to be stored in cool temperatures. And there are nearby facilities where they could be stored -- like an ice-cream factory, Bociurkiw said.
However, the facilities "are not prepared to receive" the dead, according to Bociurkiw. The crash site is large and difficult to access, nearby roads are closed and there is a lack of electricity due to the accident.
The location of some of the bodies are being marked by white flags. Civilian emergency workers told Bociurkiw that their job was to mark where the bodies were.
Moving the bodies?
"Well, that's somebody else's job," they told Bociurkiw.
How are victims' remains identified?
According to Interpol, the international police agency, it's very rare that victims can be visually identified. Interpol uses identifiers such as fingerprints, dental records or DNA samples to confirm who was on board the plane.
The agency said on Saturday that it will be deploying a team to provide "on-site assistance" within the next two days.
Dutch authorities have sent a team of at least 80 police to visit with families and gather information about the victims -- including DNA, tattoos, dental records and other specifying information.
CNN's Antonia Mortensen contributed to this report