Little is known about the ethnic Hmong people, and even less about those rumoured to be fighting a low-level war against the Lao Government.
By Kate McGeown
BBC News Online
But what seems certain, according to numerous human rights reports, is that many of the Hmong in Laos have a poor standard of living, and often feel marginalised by the authorities.
"There's a kind of fault line which separates the Hmong from the rest of the population," said Sunai Phasuk, a political analyst for human rights group Forum Asia.
The Hmong are a little-known people in a secretive land
"They are treated like traitors by the authorities," he told BBC News Online. "They are blamed for siding with the foreign imperialists."
The problem stems from the Vietnam War, when large numbers of ethnic Hmong sided with the United States army, as the conflict spread from Vietnam into neighbouring Laos and Cambodia.
The Hmong became an integral part of a secret CIA-trained militia that helped dismantle communist supply lines.
But at the end of the war, the US Government stopped its support for the Hmong.
In 1975, the communist Pathet Movement ousted the US-backed Lao royal family, and took control of the country.
Fearing the worst, as many as a third of the Hmong population are thought to have left the country.
Many settled in the United States, while others went to Thailand, Vietnam, France and Australia.
But the 300,000 left in Laos have had to deal with the consequences of backing the losing side.
According to Sunai Phasuk, the Lao Government often accuses the Hmong of being the cause of the country's problems, such as the high levels of deforestation and widespread cultivation of opium.
Many Hmong are also being forced to relocate from their highland homes to areas with poor agricultural potential, he said.
"It's a totally different way of life, and it's difficult for them to adapt," he said.
A spokesman for the human rights group Amnesty International said that Hmong people in detention were often treated unfavourably compared with other prisoners.
"Prison conditions in Laos are really awful, and the Hmong are particularly badly treated," said Amnesty spokesman Daniel Alberman.
But there is increasing evidence that the Hmong are fighting back.
Over the last few decades, there have been persistent rumours of rebel fighters living in remote jungle areas - the kind of reports which the three foreigners now on trial were trying to confirm.
Sunai Phasuk says it is very difficult to get accurate information about the number of rebels in Laos, or the activities they are engaged in.
But last month Andrew Perrin, a journalist from Time Asia magazine, managed to gain access to a remote rebel camp, where he met hundreds of Hmong families.
Three foreigners were arrested while researching the Hmong in 2003
"What we found really surprised us. There were 800-900 people - far more than we had thought - and we were told there were another 20 similar groups around Laos," he told BBC News Online.
The group he encountered was living in a state of constant siege, with women and children in desperate need of food and medical attention - and constantly on the run from the Lao authorities.
"These people are hunted like wild animals," said Mr Perrin. "It has been going on for nearly 30 years."
"From their hill-top camps, military patrols fire rockets into the jungle. If they spot someone, they shoot."
In public, the Lao Government denies that the Hmong rebels exist.
But diplomatic sources have said that, behind the scenes, the authorities believe the rebels are behind a spate of recent ambush attacks on buses in the region.
Sunai Phasuk said it was not in the government's interest to openly blame the Hmong for the attacks, as it would imply the authorities were no longer in control of the situation.
So, instead, the attacks are blamed on "bandits" or "bad people".
Amnesty's Daniel Alberman rebuffed that explanation.
"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.