Other passengers on the flight said that Mr. McAfee, 67, was escorted off the aircraft before everyone else.

Maria Claridge, a 36-year-old photographer from Fort Lauderdale, Fla., said, “He walked very peacefully, chin up. He didn’t seem stressed.”

She said he was well dressed, in a black suit and white shirt, and appeared to be traveling alone.

An F.B.I. spokesman in Miami, James Marshall, said in an e-mail that the agency was not involved with Mr. McAfee’s return to the United States. Authorities from Customs and Border Protection, Immigration and Customs Enforcement, the United States Marshals office and the United States attorney’s office did not immediately respond to questions about whether Mr. McAfee would be questioned or detained. They said there was no active arrest warrant for Mr. McAfee that would justify taking him into custody.His expulsion from Guatemala marked the last chapter in a strange, monthlong odyssey to avoid police questioning about the November killing of American expatriate Gregory Viant Faull, who lived a couple of houses down from McAfee’s compound on Ambergris Caye, off Belize’s Caribbean coast.