Mr. Duncan had lived in the neighborhood, called 72nd SKD Boulevard, for the past two years, living by himself in a small room that he rented from the Williams couple. He had told that them and his neighbors that his son lived in the United States, played baseball, and was trying to get him to come to America.

For the past year, Mr. Duncan had worked as a driver at Safeway Cargo, the Liberian customs clearance agent for FedEx, said Henry Brunson, the company’s manager. In a statement, FedEx said that Mr. Duncan was employed as a personal driver for the company’s general manager, not to work for FedEx’s global operations.

In an office with a large FedEx sign outside the building in downtown Monrovia, Mr. Brunson said that Mr. Duncan quit abruptly on Sept. 4, giving no reason. But Mr. Brunson said he knew that Mr. Duncan had family members in the United States as well.

“His sister came from the United States and he asked for a day off so that he could go meet her at the Mamba Point Hotel,” Mr. Brunson said, mentioning a hotel popular among foreigners. “He quit a few weeks after that.”

The way Mr. Duncan appears to have been infected with the Ebola virus is typical in Monrovia, where the epidemic is spreading rapidly and most people are dying at home because of a lack of ambulances and Ebola treatment centers. At home, they spread the virus to family and friends who are taking care of them.