Rainforest activist and his wife were ambushed and shot dead in the Amazon state of Para in northern Brazil on Tuesday.
Joao Claudio Ribeiro da Silva, a rubber tapper and ecologist, and his wife Maria do Espirito were killed as the country's Congress is debating a bill related to stopping deforestation.
It was not clear who shot the couple but da Silva had faced death threats from loggers and cattle ranchers, said a report by Reuters.
The couple was active in the organization of forest workers that was founded by the conservationist Chico Mendes, who was also assassinated by the ranchers in 1988.
Da Silva, a well-known figure at local and international seminars on Amazon protection, worked in defense of forest dwellers who make a living by extracting nuts, rubber and fruits.
His death has pointed out serious concerns over the violent conflicts which surround the natural resources in Latin America.
Officials reported last week that there was a sharp rise in deforestation that environmentalists said was likely fueled by the new bill.
Dozens of people are killed in land disputes, many in the sparsely policed Amazon region of Brazil, says the report.
President Dilma Rousseff ordered a probe into the murders of Da Silva and his wife.