The head of Australia's transport safety body has warned there will be no quick answers to the downing of MH17, saying it could take up to a year to complete an investigation.
The Australian Transport Safety Bureau dispatched two senior investigators to Kiev on Monday to assist an international inquiry into the disaster.
But chief commissioner Martin Dolan dampened expectations of a speedy determination. "We normally say as investigators it can take up to a year to get a firm result," he told reporters at Canberra airport.
"It's quite possible that there will be no quick response to this." Mr Dolan said it was "disappointing and upsetting" to see Russian-backed rebels tampering with evidence at the crash site in eastern Ukraine, which has been a target of international condemnation since last week's crash.
However, he hopes basic information will still be available to investigators, whose work will be coordinated by Ukrainian authorities.
Paul Ballard, one of the two ATSB officers deployed to the Ukraine, voiced concerns about the safety of investigators in a war zone. But he is philosophical about the way the site has been treated by rebels.
"We've got to understand this isn't a site within Australia, so it will get treated in the manner that it does in those countries," he said.
Prime Minister Tony Abbott has described the scene as "more like a garden clean-up than a forensic investigation".