Mr. Moura was sentenced two weeks ago to 30 years in prison after being found guilty of collaborating with Mr. Galvão.

The trials were seen as a litmus test for Brazil’s ability to begin to end the lawlessness that reigns in the Amazon region, an area the size of the United States west of the Mississippi River. The government has little presence in the area, and illegal deforestation and illegal mining are rampant.

According to the Catholic Land Pastoral, a watchdog group that tracks rural violence in Brazil, 1,546 people were killed in land conflicts in the past 25 years, usually by gunmen paid by ranchers with land claims at stake.

“The vast majority of these crimes are met with absolute impunity by the legal system,” said Antonio Canuto, an official with the group. “Today’s trial is a nearly singular fact, and it is of supreme importance to set a precedent to stop the violence.”

According to a report Catholic Land Pastoral delivered to the Justice Ministry on Thursday, of the 1,546 killings, only 85 cases were judged, Mr. Canuto said. A total of 20 plotters were found guilty, but only Mr. Moura and Mr. Galvão are behind bars. The rest either escaped from prison or are free on appeals.