It was so cold that morning in February 1962 that cigarette smoke hung in the air over the officials huddled at opposite ends of the Glienicke Bridge on the Havel River in southwest Berlin.

In one group was Francis Gary Powers, the U.S. Air Force U-2 pilot who had been shot down in 1960 by a Soviet missile and convicted by the Russians of spying. In another was Rudolf Abel, a KGB operative who had been living in Brooklyn in 1957 when he was arrested by the FBI. He, too, had been convicted of espionage.

Not far away at Checkpoint Charlie, the barrier between East and West Berlin, waited the American family of graduate student Frederic L. Pryor, the third player in the Cold War exchange that was later dramatized in the Steven Spielberg film Bridge of Spies. He was accused by police of gathering economic data needed by the West to destabilize the Communist bloc, but he said it was just for a Ph.D. thesis.

At 8:28 a.m. on Feb. 10, there was movement on the bridge. Looking straight ahead, Powers and Abel kept walking until they were back with their own countrymen. “No one died. No one took a picture,” Giles Whittell wrote in his 2010 book, Bridge of Spies.

But no one could leave, either, until Mr. Pryor was reunited with family. At 8:50 a.m., word came that he had been freed. One of the most famous prisoner exchanges of the Cold War was history.

“I couldn’t allow myself to be anything but a passive observer. It was like participating in a stage play,” Mr. Pryor said of the moment.

Mr. Pryor, who returned home and spent 32 years as an economics professor at Swarthmore College, died Monday, Sept. 2, at White Horse Village, Newtown Square, of complications from several strokes. The former Swarthmore resident was 86.

In announcing his death to the college community, president Valerie Smith said Mr. Pryor was active on campus, even after retiring in 1998. “Fred is remembered for his quick wit, broad intellectual interests, and prodigious research,” Smith said.

Mr. Pryor wrote 13 books and 120 scholarly articles. His writings focused on a range of economic systems, including chimpanzee groups, hunter-gatherer tribes, feudal agricultural societies, and capitalist and communist countries.

Son Daniel A. Pryor said his father had been a doctoral student in economics at Yale University when he decided to study at the Free University of Berlin and write his dissertation there. To complete the analysis of Soviet foreign trade. Mr. Pryor interviewed 35 experts in East Germany.

“One of the issues that wasn’t clear was whether the things that he was asking for were a state secret,” his son said. “He was doing all this work on the Communist foreign trade system, so the West would know how to destroy the East Germans; that was the theory the police had.

“But no, he was doing his dissertation. He was not at all a spy. He was in the wrong place at the wrong time.”

When the thesis was done in August 1961, he drove his red Karmann Ghia to East Berlin to give a copy to colleagues who had helped with the work. One, a typist named Eleonora, had left for the West, and her apartment had been staked out by the East German secret police.

He was arrested on charges of helping her escape and attempting to recover her possessions, Whittell wrote.

After six months of interrogations in an East German prison, Mr. Pryor had begun to despair. He didn’t know he would be let go until the morning of his release. Afterward, he told the press, “I would like to resume a normal life.”

Born in Owosso, Mich., he and his twin brother, Millard, grew up in Mansfield, Ohio, and graduated from Mansfield Senior High School in 1951. He earned a bachelor’s degree in chemistry from Oberlin College in 1955.

He spent the year after graduation living and working in South America and Europe, including a three-month stint on a commune and a job tending engines on a freighter.

After the prisoner exchange, he received a doctorate in economics from Yale. He taught at the University of Michigan and Yale before joining the Swarthmore College faculty in 1966.

In 1964, he married Zora Prochazka, an economist he had met at an American Economic Association meeting.

Outside his academic work, Mr. Pryor enjoyed experiencing different cultures. He and his wife traveled widely and lived abroad for several years. He had a playful, humorous side.

For many years, he served as a trustee for Miles, Wilberforce, and Tougaloo, all historically black colleges.

His wife died in 2008 and his brother in 2005. Besides his son, he is survived by three grandchildren.

Services are private.