BELEM, Brazil — A Brazilian rancher was found guilty yesterday of ordering the killing of an American nun and rain forest defender, Dorothy Stang, a judge announced following a two-day trial.

Vitalmiro Bastos de Moura was convicted of masterminding the killing of 73-year-old Dorothy Stang, on February 12, 2005, along a muddy stretch of road deep in the rain forest.

Judge Raymond Moises Alves Flexa sentenced Mr. Moura to 30 years in prison, the maximum sentence in a case seen as a crucial test of whether the government could crack down on lawlessness in the Amazon.

Stang, a naturalized Brazilian originally from Dayton, Ohio, helped build schools and was among the activists who have tried to defend the rights of impoverished and often exploited farmers drawn to the Amazon region.

She also attempted to halt the rampant jungle clearing by loggers and ranchers that has already ripped away some 20% of the forest cover.

Human-rights defenders said the trial is a test of whether the powerful masterminds behind land-related killings can be held accountable in the Amazon state of Para. Of nearly 800 such killings in Para during the past 30 years, only four masterminds have been convicted and none are behind bars.

Shortly after Stang ‘s killing, President da Silva ordered the army into the region, suspended logging permits, and ordered large swathes of rain forest off-limits to development.