You don't kill a load of bus passengers if you're a bandit," he said.
Andrew Perrin said it was impossible to say who was behind the bus attacks.
Eyewitnesses have claimed that those responsible spoke the Hmong language and looked like ethnic Hmong.
But Mr Perrin said the Hmong he met denied being involved in any attacks. He said there was even a possibility that the military itself was behind the ambushes.
The truth of the matter is likely to remain difficult to determine, and the continuing violence could well deter others from investigating further.