Authorities in Brazil are searching for four suspects linked to the shooting death of an American nun who had campaigned for the rights of landless peasants.

Police have not named the suspects, but they believe two of them were hitmen and the other two ordered the murder of 74-year-old Dorothy Stang.

Ms. Stang was shot three times Saturday near the town of Anapu, in the Amazon state of Para.

Brazilian President Luiz Inacio Lula da Silva sent federal police to conduct an investigation.

Officials say the missionary was shot just days after she reported that she and several local farmers had received death threats.

Ms. Stang lived in Brazil for 20 years and recently won an award for her work in the Amazon region.

Some information for this report provided by AP and AFP.