|Ribeiro's killing was compared to the murder of Stang, who was shot in Para after opposing loggers [Rodrigo Fonseca]
Police in Brazil have asked a judge to order the arrest of three men suspected of involvement in the killings of two Amazon activists, Brazillian authorities have said.
Jose Claudio Ribeiro da Silva and his wife Maria were gunned down last May near a reserve in the jungle state of Para, where they taught farmers how to use land in a sustainable manner. Para is one of Brazil's most violent and lawless states.
Police spokeswoman Aycha Nunes said on Wednesday that a judge was asked to issue arrest warrants against Jose Moreira, who allegedly ordered the killings, and the suspected gunmen, his brother Lindon Johnson and Alberto Lopes do Nascimento.
All three are at large she said, and it was not clear when the judge might rule on the request.
Moreira allegedly ordered the killings because the Silvas were opposing the eviction of three families that had occupied his land in the Nova Ipixuna reserve, Nunes said.
Silva's sister Claudelice told the Globo television network's G1 website that there were other motives for the killings.
"There were a lot of people who wanted them dead because they consistently denounced environmental crimes," she said.
"Many ranchers, farmers and loggers wanted my brother and his wife to stop bothering them with their denunciations against deforestation and land grabbing."
She said the Silvas reported illegal loggers to police and federal prosecutors and confronted powerful interests that destroy the forest for the quick economic gains to be made from selling timber, or from clearing land to raise cattle or soybeans.
The Catholic Land Pastoral, a watchdog group, said more than 1,150 rural activists have been slain in Brazil over the past 20 years.
The killings are mostly carried out by gunmen hired by loggers, ranchers and farmers to silence protests over illegal logging and land rights in the environmentally sensitive region.
The group also has a list of 125 activists whose lives it says are in danger because of their opposition to loggers.