Richard C. Paddock, Jakarta, Indonesia – It was not unusual for the lawyer, Golfrid Siregar, to receive warnings and death threats, especially after he tried to halt the $1.7 billion, China-funded hydropower dam on the remote Batang Toru river. He contended that a signature on a key environmental document had been forged.
So when three strangers brought Mr. Siregar to an emergency room three weeks ago, unconscious with a severe head injury, his friends and family had trouble accepting the police's conclusion that he had crashed his motorcycle into a curb.
Mr. Siregar, 34, never regained consciousness and died on Oct. 6, three days after arriving at the hospital in Medan, Sumatra's largest city. He left a wife and a young daughter.
Human rights and environmental groups, including Amnesty International and Human Rights Watch, are calling for an investigation into whether Mr. Siregar was murdered in retaliation for his work.
"We urge you to initiate a prompt, thorough, impartial and independent investigation into the incident," wrote Usman Hamid, Amnesty International's executive director for Indonesia, in an open letter last week to Indonesia's president, Joko Widodo.
Anton Sugiono, the chief executive of PT North Sumatera Hydro Energy, which is building the dam on the Batang Toru river, said the company would support "any investigation" into Mr. Siregar's death.
"Of course, we are very sorry to hear this happened," Mr. Anton said in an interview. "We definitely had nothing to do with it at all."
He said he had never met Mr. Siregar, who worked for the Indonesian Forum for the Environment, a prominent environmental group known by its Indonesian acronym, Walhi.
Mr. Siregar's legal battle over the Batang Toru project led to a contentious relationship with the North Sumatra Police Department, the same police force that concluded his death was an accident.
Earlier this year, Mr. Siregar had filed a complaint with the North Sumatra police on behalf of a forestry expert, who alleged that his signature had been forged on an environmental assessment for the dam project. The police refused to pursue the allegation, Mr. Siregar's colleagues said.
In August, Mr. Siregar filed another complaint – with the Indonesian national police, accusing the North Sumatra police of misconduct. Around the time of his death, he had been scheduled to provide information about the case to the national police's internal affairs department in Jakarta, the capital, Mr. Hamid said in his letter to President Joko.
A spokesman for the North Sumatra police, Tatan Dirsan Atmaja, declined to discuss the case in detail but said Mr. Siregar's death was not connected to his legal or advocacy work. "It was a single-vehicle traffic accident," he said.
Mr. Anton characterizes the 510-megawatt Batang Toru hydropower project, about 750 miles northwest of Jakarta, as an environmentally friendly project that would provide needed power to Sumatra and reduce reliance on sources that emit more carbon into the atmosphere, like diesel.
But many environmental groups argue that the dam's potential harm to the newly identified Tapanuli species of orangutan, along with other endangered wildlife in the area, far outweighs any benefit in reduced emissions.
The project, which is already under construction and scheduled for completion in 2022, would initially take up about 1,600 acres in the orangutan's historic habitat. Once the work is finished and the area reforested, its final footprint would be about 300 acres, according to North Sumatera Hydro Energy, whose name uses an alternate spelling of Sumatra.
With the flooding of the steep Batang Toru gorge, about 150 acres of the site would be underwater, an area smaller than the reservoirs of typical hydropower dams.
The Bank of China, a major Chinese state-owned bank, is financing the project. Mr. Anton said it was not part of the Belt and Road Initiative, China's ambitious program to finance infrastructure projects around the world, which has been criticized for saddling developing countries with debt.
Planning for the dam project had been underway for a decade when scientists determined in 2017 that orangutans living in the Batang Toru ecosystem constituted a distinct species, which they named the Tapanuli after the area where it lives.
There are only about 800 Tapanuli, making it the most endangered of the three orangutan species. Sumatran orangutans number about 14,600 and Borneo orangutans about 105,000, experts say.
Many Indonesian and international environmental groups fear that the Batang Toru project is endangering the Tapanuli orangutan by continuing the fragmentation of its habitat and opening the area to illegal logging and other human encroachment.
"The risks attached to the dam are incredibly severe," said Helen Buckland, director of the United Kingdom-based Sumatran Orangutan Society. "The fear is if the dam construction goes ahead, it will lead to the functional extinction of the species."
Mr. Anton has pledged to minimize harm to the orangutans, but opponents of the project see his company as ruthless and heavy-handed, citing the forgery alleged by Mr. Siregar as one example.
Mr. Siregar's client, Onrizal, a forestry expert who like many Indonesians uses one name, had signed off on a 2014 assessment of the dam's environmental impact, but he later came to oppose the project. Earlier this year, he discovered that his signature had been attached to a new report, in 2016, without his permission.
The energy company says that was a mistake, not a forgery. Mr. Anton said the 2016 filing was merely an addendum to the original report signed by Mr. Onrizal, and that it did not supersede it.
Mr. Onrizal, a scientist at the University of North Sumatra, declined through an associate to be interviewed, citing a fear of retribution.
Colleagues of Mr. Siregar say that on the evening of Oct. 2, he visited his uncle's house in Medan, drank tea and left at about 11 p.m. Around that time, a video camera captured him riding his motorcycle while wearing his helmet, they say.
At about 1:15 a.m., the three men brought Mr. Siregar to the hospital, saying they had found him lying in the street. They were later arrested on suspicion of stealing his belongings, but the police concluded that they were not responsible for his injuries. The police also said Mr. Siregar had been drinking, though they did not specify his blood alcohol level or release an autopsy report.
Colleagues and family members have raised numerous questions, including why no blood was found at the scene and why Mr. Siregar's body did not have marks and abrasions typical of a motorcycle accident. They also question why no one found his helmet, which they say he always wore. His motorcycle had little damage, they said.
Given these circumstances, they suggest he was attacked elsewhere, and that his body and motorcycle were left in the road to make it appear that he had crashed.
"How much did he drink? Before he was found, what actually happened?" asked Dana Prima Tarigan, director of Walhi North Sumatra. "It is too soon to conclude that this was due to a single-vehicle traffic accident while there are still so many mysteries that need to be revealed."
Mr. Siregar had become known as a fighter, and his fellow advocates have no intention of letting his case rest.
"He was smart. He was courageous. He was bold," said Andreas Harsono, senior Indonesia researcher at Human Rights Watch. "His death under suspicious circumstances demands a prompt, thorough investigation of all those implicated."
[Muktita Suhartono contributed reporting.]