How to Investigate AirAsia's Underwater Crash Scene

— -- Now that investigators believe they have zeroed in on the crash area for the missing AirAsia jetliner, they will treat the area like a crime scene as they first try to recover bodies and then determine whether they will have to raise the submerged plane to find out what caused the catastrophe, a veteran crash investigator told ABC News.

Six bodies have been retrieved so far, an Indonesian official told reporters early Wednesday at news conference in Indonesia. In addition, searchers have found debris including an emergency door from the doomed AirAsia Flight QZ8501 that plunged into the Java Sea Sunday with 162 people on board.

David Mearns, an underwater recovery expert and director of the Blue Water Recovery, said that the debris could help investigators track down the main crash site.

Mearns said the ships searching for the wreckage can use complex computer algorithms to track the origin of the debris and find the site where plane likely hit the water. Once the main crash site is located, a large operation will start to recover the black boxes and map the entire area.

“Forensically, they treat the whole site like a crime scene,” said Mearns. “Before they start moving anything from the site they’ll want to make sure it’s mapped.”

Even the wreckage pattern on the sea floor can help investigators understand what happened. Mearns said if it’s “in a tight area or a few hundred meters by a few hundred meters,” investigators know the plane likely hit the water intact.

If it’s spread over kilometers, investigators could assume the plane broke up at a high altitude, said Mearns.

The important mission right now is to recover the so-called black boxes that will reveal the cockpit voice recorder and the flight data recorder, said Mearns. If those are recovered the experts can start to piece together what caused the plane to plummet 32,000 feet.

The boxes are each equipped with underwater “pingers” that are built to work for 30 days underwater.

“They won’t pick anything up until they’ve mapped the site and got the bodies out…and they’ve recovered the black boxes and downloaded the data,” said Mearns.

Mearns said investigators may choose to leave large portions of the wreckage underwater if they do not feel they will be helpful for the investigation.

If the investigation starts point to a clear cause such as specific engine malfunction, officials may decide to only pick up related components.

“It will guide them to how much of the plane they want to recover,” Mearns said of the black boxes. “They don’t need to pick up every single piece of the plane.”

Mearns said if crash’s cause remains a mystery, investigators will likely work to bring up major portions of the plane to study. In that case large ships equipped with cranes may be called in to haul up heavy items such as the tail section of the aircraft where they can be reconstructed in hangars on land.

In previous crashes that were not easily solved, large portions of the plane were painstaking reconstructed to figure out what could have caused the crash.

The 1996 crash of TWA 800 off the coast of New York was found to be caused when a spark ignited a center fuel tank, but investigators spent years reconstructing the fuselage in a giant hangar in Long Island to understand what caused the fatal spark.

The Pan Am flight 103 that was detonated over Lockerbie, Scotland, was also largely reconstructed from scattered chunks of the plane, producing evidence that it was blown up by Libyan terrorists.