Two held over killings of José Cláudio Ribeiro da Silva and Maria do Espírito Santo, who were dedicated to saving the rainforests

Police in the Brazilian Amazon say they have arrested two men in connection with the murders of two rainforest activists who were gunned down in May.

José Cláudio Ribeiro da Silva and his wife, Maria do Espírito Santo, were killed on 24 May, six months after Ribeiro da Silva had predicted during an international environmental conference that he could be killed at any time.

The activists were known for their vocal stance against illegal loggers, cattle ranchers and charcoal producers operating in Praia-Alta Piranheira, a remote Amazon settlement in Brazil's Para state, where they lived.

On Sunday, nearly four months after the killings, police said they had arrested two of their three prime suspects during a dawn raid on a jungle camp around 32 miles from the Amazon town of Novo Repartimento. Police said they had seized three revolvers and one shotgun during the raid.

"The family's reaction is happiness, happiness, happiness," Ribeiro da Silva's sister Claudelice Silva dos Santos told the Guardian on Monday, as the two suspects were reportedly transferred by helicopter to a prison in Belem, the state capital. "We have been waiting for this news for nearly four months."

Police named the prisoners as José Rodrigues Moreira, who is accused of ordering the killings, and his brother Lindon Johnson Silva Rocha, who allegedly carried out the executions.

"Hidden in a tent in the middle of the forest, the two brothers were armed and even tried to escape as they were being surrounded by police," security authorities said in a statement.

Alberto Lopes do Nascimento, the third man wanted for the assassinations, had not been arrested, family members said.

Ribeiro da Silva and Do Espírito Santo were often threatened with death threats because of their fight to protect the environment, and last November the former told a TEDx conference in Manaus that he expected to be killed. "I will protect the forest at all costs. That is why I could get a bullet in my head at any moment," he said.

Their murders, six months after Ribeiro da Silva's speech, triggered widespread outrage in Brazil and made headlines around the world. The country's president, Dilma Rousseff, ordered a police investigation into the killings and hundreds of paramilitary troops were deployed in the region.

Silva dos Santos, Ribeiro da Silva's youngest sister, described the arrests as the "second step" towards justice. "Now we want convictions," she said.

She said she hoped police investigations would continue, to establish whether the murders were part of a wider conspiracy. "We believe there are more people involved [in the murders]," she said.