Brazilian activists and residents gathered Monday to pay tribute to an American nun who was shot and killed in the Amazon jungle - a region she had spent decades defending.

The service for 74-year-old Dorothy Stang came as Brazilian officials said they are looking for four suspects linked to her murder Saturday near the eastern Amazon city of Anapu.

Police have not named the suspects, but they believe two of them were hitmen, while the other two ordered the murder. An investigation is underway.

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. She had campaigned for the rights of landless peasants in the environmentally fragile region.

Some information for this report provided by AP and Reuters.