(Washington, DC) – Honduras should ensure that its investigation into the killing of the indigenous leader and environmental-rights activist Berta Cáceres is exhaustive and unbiased, Human Rights Watch said today.

In the early hours of March 3, 2016, gunmen broke into Cáceres’s home in La Esperanza, Intibuca, and shot her dead, media accounts said. The killers escaped without being identified. Cáceres’s family and colleagues have said they believe that she was murdered because of her work on behalf of indigenous and environmental rights.

“A thorough and impartial investigation is absolutely critical to ensure that those responsible for Cáceres’s death are brought to justice,” said José Miguel Vivanco, Americas director at Human Rights Watch.

Cáceres, a member of the Lenca indigenous group, cofounded the Civic Council of Popular and Indigenous Organizations of Honduras (COPINH) and led a campaign against the construction of the Agua Zarca Dam on the Gualcarque River. The Chinese state-owned company Sinohydro, the world’s largest dam builder, pulled out of the construction in 2013, publicly citing “ongoing community resistance and outrage.”

Several COPINH members have been attacked and killed during protests, but no one responsible for the attacks has been brought to justice. Cáceres herself had received multiple death threats, media accounts said. In 2009, the Inter-American Commission on Human Rights (IACHR) asked the Honduran government to adopt measures to guarantee her safety, but the threats continued.

At a news conference last week, Cáceres said that four community leaders opposed to the dam had been killed since 2013 and that several others had received threats. On February 20, security forces detained more than 100 people who participated in a COPINH protest near the Agua Zarca Dam site, the New York Times reported.

Cáceres was awarded the 2015 Goldman Environmental Prize for South and Central America, which honors grassroots leaders for efforts to protect the natural environment. Upon receiving the prize, she said, “they follow me. They threaten to kill me, to kidnap me. They threaten my family. This is what we face.”