The Try Pheap Group did not respond to a list of emailed questions.

Sao Sopheap, a spokesman for the Environment Ministry, said the government was working with international conservation groups to eliminate illegal logging inside land concessions. But he added that land-reform measures, including a 2012 moratorium on new concessions, were not a response to pressure from activists.

“Those activists concentrating on advocacy are probably not very helpful,” Mr. Sopheap said in a telephone interview, without mentioning Mr. Leng. “They probably are working on propelling their own interests.”

Mr. Leng was born in 1975, just as the Khmer Rouge began a four-year reign of terror in Cambodia that left an estimated 1.7 million people dead. His family was forcibly relocated from Takeo Province, near Phnom Penh, to the northern province of Preah Vihear, on the border with Thailand.

In the early 1980s, the family survived by selling rattan it harvested in nearby forests and eating wild fish and game. “I fell in love with the forest and the land because they were our only way to survive,” Mr. Leng, who has a boyish face and speaks with a rapid-fire delivery, said during an interview at his home on the dusty outskirts of Phnom Penh.

After graduating from law school in 1997, Mr. Leng said, he worked for more than a decade as an investigator for two Cambodian human rights groups and later on a forest-mapping project funded by the United States Agency for International Development. But he said his work had often prevented him from doing what he was determined to do: aggressively fight illegal logging.

He began working independently about five years ago and has spent months posing as a cook or a logger and hanging out with company employees to gain access to forests and logging camps within timber concessions. His reports are based on his covert photos and videos, along with documents from local journalists, civil servants and other informers that he analyzes at his home office, he said.

A primary goal, he added, is to determine how the illegal logging that he witnesses is linked to the global timber supply chain and the Chinese, Vietnamese and Cambodian investors behind the logging projects.