Fortify Rights, a nonprofit organization registered in the United States and Switzerland, was formed in 2013 by Mr. Smith and fellow human rights activists. It has focused on investigating human rights abuses in Southeast Asia, particularly Myanmar.

Beginning in October 2016, Myanmar’s military and local officials methodically removed sharp tools that could be used for self-defense by the Rohingya, destroyed fences around Rohingya homes to make military raids easier, armed and trained ethnic Rakhine Buddhists, and shut off the spigot of international aid for the impoverished Rohingya community, the Fortify Rights report says.

Most of all, more troops were sent to northern Rakhine State, where the bulk of the largely stateless Rohingya once lived. Fortify Rights says that at least 27 Myanmar Army battalions, with up to 11,000 soldiers, and at least three combat police battalions, with around 900 personnel, participated in the bloodletting that began in late August and continued for weeks afterward.

United States officials have said that the violence amounted to a calculated campaign of ethnic cleansing, and one United Nations official described the anti-Rohingya campaign as bearing “the hallmarks of genocide.”

The Fortify Rights report suggests an alternate story line to the suggestion that the military-led atrocities, which were often abetted by ethnic Rakhine locals armed with swords, were solely a response to attacks by Rohingya militants on army and police posts on Aug. 25, 2017.