In March 2016, gunmen burst into the house where she was staying in La Esperanza, her hometown in western Honduras, and fatally shot her.
The Honduran government has been under intense pressure to find Ms. Cáceres’s killers. The murder occurred as President Juan Orlando Hernández was trying to project a new image of his country, one of the most violent in the world.
The other suspects arrested and tried in the killing included company employees, hired assassins and members of the army. In 2016, four other suspects were arrested in raids, two of whom were linked to Desa. One of the suspects arrested, Sergio Rodríguez Orellana, was a manager for social and environmental issues for Desa, and a second, Douglas Geovanny Bustillo, had worked in the past for a security company hired by the dam project.
In a statement, Desa defended Mr. Castillo and its employees, saying they were “totally unconnected” to the crime. It accused the authorities of “unjust detention” resulting from “international pressure and campaigns by diverse NGOs to discredit the company.”
Desa also questioned the fact that the arrest came two years to the day after Ms. Cáceres’s killing, according to Reuters.
Members of the activist’s family said they were sur of Mr. Castillo’s guilt. “There is no doubt that he was one of the material authors of Berta’s death,” said her ex-husband, Salvador Zuniga, according to The Associated Press.
Mr. Castillo is the second captured suspect accused of having been a mastermind in the murder. The other suspects arrested and tried in the killing included company employees, hired assassins and members of the army.
Honduras has seen repeated confrontations between members of indigenous groups and mining or hydroelectric operations. Mr. Hernandez, who won re-election in December in a vote marred by accusations of fraud, has sought to boost investment in such ventures.
Members of Copinh, an activist group that Ms. Cáceres founded, gathered on Friday in front of prosecutors’ offices in Tegucigalpa, the capital, to demand the arrest of more prominent local businessmen who they accuse of being connected to her killing.
“The owners of Desa killed my mother,” said Olivia Zuniga Cáceres, her daughter, who is a lawmaker with the Liberty and Refoundation Party, according to The A.P. She said she was fighting in Parliament to halt the construction of the Agua Zarca Dam.
In October, an international team of lawyers issued a report that said Ms. Cáceres’s killing had been planned for months, and that the plot involved company employees, private security forces and agents of the state.
The report, based on an outside review conducted at the request of Copinh and the slain woman’s family, suggested that the dam company’s leadership had ordered her assassination and concluded that it was “not an isolated incident.”
A Mexican activist, Gustavo Castro Soto, was wounded in the attack that killed Ms. Cáceres.
Per capita, Honduras is the deadliest country on the planet for environmental activists, according to the London-based watchdog Global Witness. The group said in July that 14 had been killed there in 2016, including Ms. Cáceres and two other members of her organization.