Claudelice Silva dos Santos was shocked but not surprised when her brother and his wife were murdered. For years José Cláudio Ribeiro da Silva and Maria do Espírito Santo da Silva had been on the receiving end of death threats and attacks for their work combatting illegal logging and deforestation in Brazil’s Amazon rain forest, where they lived. “We knew that there was a high risk that it could happen,” Santos says. “But we always believed that it never would happen, that the resistance, the visibility of our fight—all the things we did to prevent the killing—would work out.”

Santos’s relatives were among more than 1,500 people across 50 countries to be murdered in retaliation for protecting land, water, forests and other natural resources between 2002 and 2017. The annual death toll doubled over that 15-year period, and the killings tended to take place in countries with high levels of corruption and weak rule of law, according to study findings published Monday in Nature Sustainability. As the authors report, in that period, murders of environmental defenders outweighed the combined deaths of soldiers from the U.K. and Australia deployed to overseas war zones.

“These cases include everything from award-winning people who were successful in garnering international support to others who were very much operating at the local level,” says Mary Menton, a research fellow in environmental justice at the University of Sussex in England and a co-author of the new study. “Oftentimes it’s individuals killed, but there have also been cases of massacres.”

The study relied on a database of murders of environmental defenders compiled by Global Witness, a nonprofit organization dedicated to exposing corruption and environmental abuse. Global Witness verifies each entry in its database through three separate sources, including media stories, local nongovernmental organization reports and interviews with residents of the affected areas.

The researchers performed a geospatial analysis of 683 deaths that occurred between 2014 and 2017 (in 2018 another 164 environmental defenders lost their lives, according to a report Global Witness published last week). They overlaid the Global Witness data with data pertaining to agricultural harvests, forest cover, mining and dams to see whether the prevalence of these activities correlated with increased murders per capita.

Central and South America are the deadliest regions in which to be an environmental defender, they found. People fighting against mining and big agriculture projects accounted for the greatest share of deaths, and countries with larger agriculture sectors and more hydroelectric dams tended to have higher numbers of murders per capita. Indigenous groups suffered the worst losses, and nonindigenous lawyers, journalists, activists, park rangers and others were killed as well.

The researchers compared murder rates with countries’ rule of law—a ranking calculated by the World Justice Project, a nongovernmental organization, that takes into account corruption, enforcement, justice, fundamental rights, security and order. They also separately compared murder rates to corruption levels, as reported by the nongovernmental organization Transparency International.

Not surprisingly, they found significant correlations between high levels of corruption, weak rule of law and the murder of environmental defenders. “This is an intuitive finding, but sometimes we think we know things, but we don’t have the evidence to back it up,” Menton says. “Now we have an evidence base to say, ‘We see this correlation not just in one country but globally.’”

Only about 10 percent of environmental defenders’ murderers are ever brought to justice, Global Witness says. Criminals may benefit from the involvement of police, government or judiciary personnel in carrying out a crime or ensuring it never gets investigated or prosecuted, Menton says. Alternatively, a country may lack the resources necessary to investigate or prosecute it. Either way, Menton adds, the situation creates an atmosphere of impunity in which “the killers essentially know they’re not going to get caught.”

Such was the case for Santos’s relatives, whose murders were never fully answered for. What she calls the “consortium of death” that claimed her brother and sister-in-law’s lives has three tiers, Santos believes: the people hired to carry out the killings, the people who organized them and the people who financed them. Those allegedly in the latter two tiers—the businesspeople, politicians and large landowners—inevitably get away with their crimes, she says, because they enjoy high-level protection through their connections with authorities (or because they are the authorities). “When justice is not carried out fully, it changes your life,” Santos says. “The only thing we can do is not panic, so we don’t stop our fight.”

According to Philippe Le Billon, a geographer at the University of British Columbia, who was not involved in the new research, the study is “a welcomed contribution to the literature and helps to draw further attention to violence against environmental defenders and the responsibilities of resource-based corporations.”

Menton agrees that companies should be pressured to uphold human rights and clean up their supply chains. “If we can show that companies are linked to killings, then they need to be held accountable for their role in that,” she says. “And not just the small, subsidiary companies but the bigger companies upstream.”

Le Billon emphasizes, however, that the data set the authors used is not exhaustive and likely contains “blind spots”—especially with regard to African countries, where Global Witness says murders are likely underreported. Menton agrees that the data do not include every relevant murder. Ones that occur in rural communities may escape notice, and some in authoritarian countries may never be publicly reported. “We’re really only starting to understand the depth of what’s going on,” she says.

Menton and one of her colleagues are now working on a project that focuses on people currently under threat and those left behind after environmentally motivated murders. They aim to better understand the drivers of violence, as well as what factors influence whether communities continue to fight in the face of intimidation, threat and, if applicable, murder. Ultimately, they hope to shed light on how to prevent killings before they happen. Menton also plans to launch an online platform for environmental defenders to safely—and, if necessary, anonymously—share their stories and amplify their voices.

“We want to say to the world, ‘You need to pay attention to this,’” Santos says. “It’s unacceptable for people to be assassinated for defending human rights and for defending a public good, the environment.”