The diamond lode deep in the Amazon rain forest promised riches. That it sat on a reservation belonging to a fierce warrior tribe seemed a mere detail to Antonio Jose Alves dos Santos.

He braved the Roosevelt River's swift currents, his gear tied tightly in a sack, to slip past federal agents guarding the reservation. He hiked through the jungle for five days, carrying two weeks' worth of food on his back.

But something snapped with the reservation's Indians. They massacred 29 "garimpeiros," as prospectors such as dos Santos are known. "They killed two men right off. Pow! Pow! Then they tied the others up in a row and slaughtered them like animals," dos Santos recalled, saying that about 200 miners were there that day.

"I escaped over a hill," he recalled, telling his story at Espigao d'Oeste, the town nearest the reservation and a gathering place for garimpeiros. He said he looked back and saw the Indians cut off one miner's head.

The bloodshed on April 7 has caused Brazil to focus on long-simmering questions: Who owns the region's mineral wealth? Whose law prevails on the reservation? How can the area's riches be tapped while preserving ancient rain-forest cultures?

The massacre came after a four-year diamond rush that saw garimpeiros flood into the reservation 2,100 miles northwest of Rio de Janeiro.

Established in 1976 and named for former President Theodore Roosevelt, who once explored the region, the reservation is densely forested and ridden with malaria. That didn't dissuade poor, mostly illiterate garimpeiros from pursuing its diamonds.

Brazil's Mines and Energy Ministry estimates $2 billion worth of diamonds have been taken off the 6.7 million-acre reservation since 1999, making it South America's largest diamond mine.

The influx of miners and their cash wreaked havoc on the culture of the Cinta Larga Indians, fueling alcoholism, drug use and sexually transmitted disease among the tribe's 1,300 members. At first, some Indians helped the miners -- after charging them a fee to enter the reservation -- but then they wanted to mine for themselves.

Under Brazilian law, mining is illegal on Indian reservations, as is the presence of most non-Indians. In 2002, the federal government cleared thousands of non-Indians from the reservation, but the miners sneaked back.

"After the garimpeiros got kicked out, they found another area to mine. The warriors would take them off, but they kept coming back," said chief Pio Cinta Larga, who, like many Brazilian Indians, uses his tribe's name for his surname.

"Finally, the warriors lost patience, and this is what happened. The killings were a warning. We don't want whites here," he said.

With four Indians in war paint behind him, Pio explained that the slayings were perfectly acceptable in Larga culture.

"We are warriors," he said. "Before the white man came, none of the tribes here were friends. We fought and killed each other; that is how we resolved things."

Historically, whites have resolved problems with the Larga through violence of their own. "Almost all the early contact between the Cinta Larga and whites has resulted in massacres. For them, that is our political language," said Carmen Junqueira, an anthropologist who worked with the tribe for eight years.

Rubber tappers massacred Cinta Larga Indians at least four times in the 1950s and '60s, with an entire village of about 30 Indians wiped out in one incident.

Federal police are considering charging Pio and 11 other Indians with the killings, but that may not be easy. Indians have a special status in Brazil. Only federal police can arrest them, and they may be found legally not responsible for their actions if deemed insufficiently acculturated.

The garimpeiros argue that Cinta Larga are just ordinary citizens, wearing modern clothes and driving fancy pickup trucks.

While some miners were shot, autopsies found most were killed with traditional war clubs or arrows, said Trajano Azevedo Fonseca of the federal Indian Bureau.

The Indians' modern dress may have misled the garimpeiros into overlooking the tribe's violent customs. It is hard to believe that Pio's tribe is thought to have only recently given up cannibalism.

Some people, such as Celio Renato de Silveira, a town councilman in Espigao d'Oeste, see the hand of a powerful "diamond mafia" that hides its illegal activities in collusion with the tribe.

Celso Fantim, of the miners' association, also blames white criminals for the massacre.

"They did this to scare away garimpeiros because they want all the diamonds for themselves," he said. "But it won't work. The garimpeiros will return because everybody here is hungry and the Indians will invite them back in for a fee."

Cinta Larga warriors massacred 29 diamond miners in April after a four-year rush flooded the Indian reservation with prospectors.