The reporting behind “Firestone and the Warlord” took place over several years in the United States, Africa, Europe and Asia.

The reporting came to include more than 200 interviews with current and former Firestone employees at all levels of the company, from the most senior executives to the laborers and domestic staff who worked on the company’s rubber plantation in Liberia. We also interviewed members of Charles Taylor’s former inner circle, including his top advisers and military operatives. As well, we interviewed former U.S. diplomats, academics, former West African peacekeepers, current and former Liberian government officials, humanitarian aid workers, union organizers, former fighters, and former leaders of warring factions in Liberia’s civil war.

The reporting process included research at the Liberian Collections Project at the University of Indiana, university libraries in Akron, Ohio, and Berkeley, Calif., the Center of National Documents and Records Agency for the Government of Liberia, and public documents at Georgia Tech collected as part of Liberia’s Truth and Reconciliation Commission.

The reporting also drew from the National Security Archive at George Washington University, the U.S. National Archives, and the libraries of former presidents Jimmy Carter, Ronald Reagan, George H.W. Bush and Bill Clinton. In 2009, with the support of the Investigative Reporting Program at UC Berkeley, we obtained hundreds of declassified cables and other records from the U.S. Department of State and the British Foreign Ministry from 1989 to 2009 relating to Bridgestone-Firestone and its rubber operations in Liberia. The cables also contained information on the conflict in Liberia, human rights violations and relief efforts in and around the Firestone plantation.

In the spring of 2014, we obtained a collection of court documents from Firestone insurance cases in Beaumont, Texas, and Summit County, Ohio, pertaining to losses incurred at the Firestone plantation in Liberia during the country’s civil war. Those court documents included formal agreements, internal company memos, correspondence between Firestone and Charles Taylor’s National Patriotic Front of Liberia, and excerpts from statements and sworn depositions taken from a range of Firestone managers and executives, Liberian rebel soldiers, military advisers and security personnel.

The court documents also included a handwritten diary of by a Firestone manager concerning Taylor’s initial invasion of the plantation in June 1990 and the formal Memorandum of Understanding signed by Firestone and Taylor’s government in January 1992.

Our reporting also drew upon a review of trial transcripts from Taylor’s war crimes trial at the Special Court for Sierra Leone in The Hague.

One of the people we interviewed at length was Gerald Padmore, a Liberian-American lawyer based in Denver, Colo., who was retained by Firestone as a consultant after Taylor’s forces captured the plantation in 1990. Just this month, Donald Ensminger, a former Firestone executive who was the Liberian plantation’s general manager in 1990 and 1991, agreed to speak publicly for the first time in 23 years about his experiences for this story.

We contacted Firestone in May 2014 to interview its officials. Firestone had offered to provide a tour of its plantation and interviews with workers who had been present during the war. But the Ebola crisis prevented this. Company representatives ultimately responded in writing to a list of questions. This month, Firestone produced seven pages of written responses to additional questions about its dealings with Taylor during the various stages of the war.

Several people who played a role in the events in Liberia in the early 1990s, and whose words and actions are reflected in this article, have since died. They are Don L. Weihe, who served as general manager on the plantation in 1992, and Peter Jon de Vos, the former U.S. ambassador to Liberia.

We were assisted in Liberia by Abel Welwean, who, with his brother Arthur, grew up on the plantation and later worked for Firestone. Arthur, a bank examiner in Georgia, provided accounts of the events on the plantation for this article.

Additional reporting, fact checking, editing and research was contributed by Marcela Gaviria, Will Cohen, Nesa Azimi, Daisy Squires, Leah Bartos, Hannah Birch, June Thomas, Ashley Gilbertson, Timothy Grucza and Rachel Anderson; Martin Foster and Tesun Oh in Japan; Clair MacDougall and Erasmus Tweh in Liberia; Ben Ezeamalu and Emmanuel Ogala in Nigeria.

In addition to the Investigative Reporting Program at UC Berkeley, Jonathan Jones’s earliest reporting was supported by the Overseas Press Club I.F. Stone Award and an Investigative Reporters and Editors Freelance Fellowship Grant.

Finally, we relied on data collected by Kristen Cibelli, Amelia Hoover and Jule Krüger of Benetech/ Human Rights Data Analysis Group. The group has published a database of victim and witness statements collected by the Liberian Truth and Reconciliation Commission. The material is convenience sample data, and as such is not a statistically representative sample of events in the Liberian conflict. This data does not support conclusions about patterns, trends, or other substantive comparisons (such as over time, space, ethnicity, age, etc.)