A convoy of eight trucks carrying wreckage from the Malaysia Airlines Flight 17 disaster arrived at a Dutch military base Tuesday, as the official investigation into the cause of the crash continues nearly five months after the plane went down in eastern Ukraine.

Flight 17 was shot down on July 17 over territory held by pro-Russia rebels, killing all 298 passengers and crew - most of them Dutch. International teams seeking to retrieve human remains and salvage evidence have had difficulty reaching the crash site due to clashes between Ukrainian and rebel forces. Six victims have yet to be identified.

Tjibbe Joustra, who heads the Dutch Safety Board that is leading the international investigation into the crash's cause, said investigators will now further photograph, scan and categorize the wreckage at the Gilze-Rijen military base in the south of the Netherlands. They plan later to reassemble part of the Boeing 777 in a hangar.

"It will take several months before we have a reconstruction of parts of the aircraft," he said.

The Safety Board said in a preliminary report in September the plane was brought down by "high-energy objects from outside the aircraft." That vague formulation has left the door open for confusion. A high-ranking rebel officer has acknowledged that rebels shot down the plane with a ground-to-air missile after mistaking it for a Ukrainian military plane. But Russian media say it is also possible the plane was shot down by a Ukrainian jet.

The Safety Board's final report may rule out one or the other scenario, but it will not seek to attribute responsibility. Meanwhile, Dutch prosecutors are coordinating an international criminal investigation, but have yet to name any suspects or say when or how charges might be brought.

Families of some victims have raised concerns about Dutch leadership of the investigation.

Bob van der Goen, whose firm Van der Goen Advocaten represents 20 family members of victims from four countries, has launched a campaign to have the Dutch government cede control over the investigation to the United Nations.

The Dutch performance so far "has been terribly amateurish," Van der Goen said in an interview Tuesday, citing the late arrival of investigators on the crash site and a failure to interview potential witnesses in Ukraine in a timely manner.

"I can understand keeping the investigation confidential, so that you don't release partial results," he said. "What I don't understand is secrecy about what it is you're undertaking, what the procedure is."

A spokeswoman for the Dutch justice ministry said it will respond to Van der Goen's criticism later Tuesday.