MEXICO CITY — It was just before midnight when two men kicked in the door to Berta Cáceres’s house in the small Honduran mountain town of La Esperanza. Moving past the kitchen, one of them opened the door to her bedroom and fired six shots. She died moments later.
In a country where the fight to protect land rights provokes violent retaliation, the murder in March 2016 of another environmental defender might simply have receded into a grim tally of regrettable losses.
But Ms. Cáceres, 44, had won international acclaim for leading her indigenous Lenca community against a dam planned on their land. Her prominence transformed her killing into an emblematic crime — and turned the investigation that followed into a challenge to the entrenched impunity of the powerful in Honduras.
Now, 20 months after the killing, a team of five international lawyers has warned that the people who ordered it may never face justice.
The evidence, the lawyers said, points to a plot against Ms. Cáceres that was months in the making and reached up to senior executives of Desarrollos Energéticos, known as Desa, the Honduran company holding the dam concession.
“The existing proof is conclusive regarding the participation of numerous state agents, high-ranking executives and employees of Desa in the planning, execution and cover-up of the assassination,” the lawyers wrote.
Desa has repeatedly denied any involvement in Ms. Cáceres’ death or any connection to “acts of violence and intimidation.”
Eight suspects are in custody, including Sergio Rodríguez Orellana, the social and environment manager for the company, and Douglas Geovanny Bustillo, a retired Honduran Army lieutenant who was Desa’s director of security until mid-2015.
“What the public ministry has yet to do is indict the people who hired Bustillo to plan the operation,” said Miguel Ángel Urbina Martínez, one of the lawyers reviewing the case at the request of Ms. Cáceres’s family. The lawyers’ report, which The New York Times has obtained, will be released Tuesday.
The government’s investigation, by an elite unit in the Honduran attorney general’s office, remains open, although the lawyers’ group said there was no sign that it had progressed beyond the eight suspects.
Two American advisers, a retired homicide detective and a former federal prosecutor, have been working with Honduran authorities since the first days of the inquiry, part of an effort by the United States Embassy to pushthe government of President Juan Orlando Hernández to solve high-profile criminal cases.
Many of those cases involve powerful groups that critics say operate beyond the law. “The great challenge for Honduras is to dismantle these parallel forces,” said Mr. Urbina, a criminal justice expert from Guatemala and an adviser on judicial reform.
To prepare the report, Mr. Urbina’s group examined some 40,000 pages of text messages, which were retrieved by Honduran government investigators from three cellphones, one seized at Desa’s offices and two used by Mr. Rodríguez and Mr. Bustillo.
The messages, according to the report, show that the two men remained in frequent contact with three high-ranking Desa executives as they tracked the movements of Ms. Cáceres and other members of her organization, the Civic Council of Popular and Indigenous Organizations of Honduras, known as Copinh.
The conversations reveal, the lawyers said, that the orders to threaten Copinh and sabotage its protests came from Desa executives who were exercising control over security forces in the area, issuing instructions and paying for police units’ food, lodging and radio equipment.
“There was this criminal structure comprised of company executives and employees, state agents and criminal gangs that used violence, threats and intimidation,” said Roxanna Altholz, the associate director of the Human Rights Law Clinic at the University of California, Berkeley, and a member of the lawyers’ group.
The other members of the legal team are a former war crimes prosecutor, Dan Saxon, and two Colombian prosecutors who have tried human rights cases, Jorge E. Molano Rodríguez and Liliana María Uribe Tirado. They have been working on the case for a year, traveling to Honduras to conduct interviews and review case material.