(CNN) -- Three suspects have been arrested in the August slaying of 12 indigenous Awa people in southwestern Colombia, the military announced Tuesday.
Empty coffins sit in Bolivar Square in Bogota, Colombia, last month during a protest against the killings.
The three men, at least one of whom is believed to belong to the Marxist guerrilla group Revolutionary Armed Forces of Colombia, were members of Los Cucarachos crime gang, Colombian Defense Minister Gabriel Silva said. Los Cucarachos are involved in drug trafficking, extortion and kidnappings, the minister said.
The robbery of 3 million Colombian pesos ($1,550) appears to have been a motive, Silva said. A group of hooded men men entered an Awa house and killed everyone inside, including women and children, Silva said at a news conference.
"That was a very dark day in the history of human rights and violence in Colombia," he said.
The suspects were not identified Tuesday because they were in the process of being charged, Silva said. He added that authorities believe the men had been working as paid assassins and narcotraffickers in the area.
A reward of about 130 million pesos ($67,500) will be divided among several people, Silva said, declining to give further information for security reasons. The defense minister said authorities have seven sources of information and seven witnesses.
One of the criminal gang's ringleaders, who goes by the alias "Freddy," eluded captured and also is believed to be involved with guerrillas from the Revolutionary Armed Forces of Colombia, known as the FARC, Silva said.
He noted that the Awa live in a remote and largely lawless area that has been engulfed in a long-running war among the FARC, government troops and right-wing militias.
Indigenous leaders don't like that combination.
"It worries us that they have taken the war to their territory," said Luis Andrade, president of the National Indigenous Organization of Colombia, known by its Spanish acronym ONIC.
The three suspects also are being investigated in other massacres of Awa, Silva said.
At least 38 Awa have been killed this year, Andrade said. The latest slayings occurred between September 13 and 23, when four men and one Awa women were killed, said Survival International, a human rights organization that supports tribal people around the world.
The 12 Awa killed in August included five children and a newborn.
"This pains our soul," Colombian President Alvaro Uribe said at the time.
More than 20 Awa were killed between February and May, said Survival International.
In all, 93 indigenous people from several tribes have been killed in Colombia this year, Andrade said.
"The situation of indigenous peoples in Colombia is incredibly precarious," said Marcelo Pollack, a Colombia researcher at Amnesty International.
About 21,000 Awa are believed to live in the rainforest on both sides of the Colombia-Ecuador border. Originally hunter-gatherers, the Awa are now more oriented toward growing some crops and raising chickens, pigs and other small animals. Development has encroached upon their territory, shrinking the area in which the Awa live.
The Awa in Colombia are not related to the Awa in Brazil, who live more than 2,000 kilometers (1,240 miles) away.
The Colombian Awa are a hard-working and peaceful tribe, said Andrade.
But they increasingly find themselves caught in the middle of the warring groups in the area, not to mention drug traffickers and common criminals.
"The Awa don't want to take sides in the conflict," said Myles Frechette, U.S. ambassador to Colombia from 1994-97. "Of course, in Colombia that's not acceptable. The crooks, and the FARC too, say, 'You're with us or you're gone.' "
News outlets reported that FARC guerillas admitted in February that they killed several indigenous people they accused of collaborating with the Colombian government.
A FARC statement about the killings was posted then by the New Colombia News Agency and Caracol Radio's Web site.
The statement said the guerrillas were not targeting indigenous populations but took the action "against people who independent of their race, religion, ethnicity, social condition etc. accepted money and put themselves at the service of the army in an area that is the object of military operations."
After the more recent killings of the 12 Awa, the Colombian government asked the United Nations High Commissioner for Human Rights to help investigate. .
Frechette says Colombia has added incentive to find whoever is killing the indigenous people because of the recent election of President Obama, who has made it known he is concerned about human rights. Colombia wants to please the United States to gain approval from the U.S. Congress for a bilateral trade agreement.
"The Colombians are doing a whole bunch of things to ingratiate themselves," Frechette said.