Prosecutors say the stunning courtroom confession of the man they say killed rain forest defender Chico Mendes was designed to protect the man who ordered the murder, the gunman's cattle rancher father.

Darci Alves Pereira, 22, startled the tiny jammed courthouse on the trial's opening day Wednesday by flatly admitting that he gunned down the rubber tapper on Dec. 22, 1988.Mendes, 44, had gained international recognition for organizing opposition to ranchers who have cleared vast swaths of rain forest for pasture, threatening a vital ecosystem as well as the livelihood of rubber tappers.

He became a symbol of Brazil's poor and landless and the trial in this far-flung Amazonian town near the Bolivian border has gripped this vast nation of 150 million people.

After Mendes stopped Pereira's father and co-defendant, Darly Alves da Silva, from clearing a tract of rain forest, the activist had repeatedly told police that da Silva planned to kill him.

The trial in Xapuri, 2,650 miles northwest of Rio de Janeiro, was to resume Thursday with opening statements and the testimony of witnesses for the defense and prosecution.

If found guilty, da Silva and Pereira would face sentences of between 12 and 30 years in prison.

Marcio Thomaz Bastos, chief lawyer for the prosecution, said Pereira's confession was a planned maneuver to spare his 54-year-old father.

"Darci is being an obedient son," Bastos said during a break. "His father told him to kill, and he killed. Now he told Darci to lie, and he's lying to protect his father."