Trundling along the dirt roads of the Amazon, the giant logging truck dwarfed the vehicle of the investigators following it.
The trunks of nine huge trees were piled high on the back - incontrovertible proof of the continuing destruction of the world's greatest rainforest and its most endangered tribe, the Awa.
Yet, as they travelled through the jungle early this year, the small team from Funai - Brazil's National Indian Foundation - did not dare try to stop the loggers; the vehicle was too large and the loggers were almost certainly armed. All they could do was video the truck and add the film to the growing mountain of evidence showing how the Awa - with only 355 surviving members, more than 100 of whom have had no contact with the outside world - are teetering on the edge of extinction.
It is a scene played out throughout the Amazon as the authorities struggle to tackle the powerful illegal logging industry. But it is not just the loss of the trees that has created a situation so serious that it led a Brazilian judge, Jose Carlos do Vale Madeira, to describe it as "a real genocide".
People are pouring on to the Awa's land, building illegal settlements and running cattle ranches. Hired gunmen - known as pistoleros - are reported to be hunting Awa who have stood in the way of land-grabbers.
Members of the tribe describe seeing their families wiped out.
Human rights campaigners say the tribe has reached a tipping point and only immediate action by the Brazilian Government to prevent logging can save the tribe.
Survival International is starting a campaign to highlight the plight of the Awa, backed by Oscar-winning actor Colin Firth. In a video to be launched today, Firth will ask the Brazilian Government to take urgent action to protect the tribe.
The 51-year-old, who starred in The King's Speech, delivers an appeal on camera at the end of the film calling on Brazil's Minister of Justice to send in police to drive out the loggers.
The Awa are one of only two nomadic hunter-gathering tribes left in the Amazon. According to Survival, they are now the world's most threatened tribe, assailed by gunmen, loggers and hostile settler farmers.
Their troubles began in earnest in 1982, with the inauguration of a European Economic Community and World Bank-funded programme to extract massive iron ore deposits found in the Carajas mountains. The EEC gave Brazil US$600 million to build a railway from the mines to the coast, on condition that Europe received one-third of the output, a minimum of 13.6 million tonnes a year for 15 years.
The railway cut directly through the Awa's land and with the railway came settlers. Road-building quickly followed, opening up the Awa's jungle home to loggers.
It was, according to Survival's research director, Fiona Watson, a recipe for disaster. One-third of the rainforest in the Awa territory in Maranhao state in northeast Brazil has since been destroyed and outsiders have exposed the Awa to diseases against which they have no immunity.
"The Awa and the uncontacted Awa are really on the brink," she said. "It is an extremely small population and the forces against them are massive. They are being invaded by loggers, settlers and cattle ranchers. They rely entirely on the forest. They have said to me: 'If we have no forest, we can't feed our children and we will die."'
But it appears that the Awa also face a more direct threat. Earlier this year an investigation into reports that an Awa child had been killed by loggers found that their tractors had destroyed the Awa camp.
"It is not just the destruction of the land; it is the violence," said Watson. "I have talked to Awa people who have survived massacres. I have interviewed Awa who have seen their families shot in front of them. There are immensely powerful people against them. The land-grabbers use pistoleros to clear the land. If this is not stopped now, these people could be wiped out. This is extinction taking place before our eyes."
What is most striking about the Funai undercover video of the loggers - apart from the sheer size of the trunks - is the absence of jungle in the surrounding landscape. Once the landscape would have been lush rainforest.
Now it has been clear-felled, leaving behind just grass and scrub and only a few scattered clumps of trees.
"They are chopping down wood and they are going to destroy everything," said Pire'i Ma'a, a member of the tribe. "Monkeys, peccaries, tapir, they are all running away. I don't know how we are going to eat - everything is being destroyed, the whole area.
"This land is mine, it is ours. They can go away to the city, but we Indians live in the forest. They are going to kill everything. Everything is dying. We are all going to go hungry, the children will be hungry, my daughter will be hungry, and I'll be hungry, too."
In an earlier interview with Survival, another member of the tribe, Karapiru, described how most of his family were killed by ranchers. "I hid in the forest and escaped from the white people. They killed my mother, my brothers and sisters and my wife.
"When I was shot during the massacre, I suffered a great deal because I couldn't put any medicine on my back. I spent a long time in the forest, hungry and being chased by ranchers. I was always running away, on my own. I had no family to help me, to talk to.
"So I went deeper and deeper into the forest. I hope when my daughter grows up she won't face any of the difficulties I've had.
"I hope everything will be better for her. I hope the same things that happened to me won't happen to her."