Mark Kennedy, a British police officer who spent seven years infiltrating environmental and activist groups while working undercover for the Metropolitan Police force in London, may have monitored an American computer scientist and spied on others while in the United States.

The computer scientist, Harry Halpin, said that he was at a gathering of activists and academics in Manhattan in January 2008 that Mr. Kennedy — then using the pseudonym Mark Stone — also attended. He said Mr. Kennedy collected information about him and about a man and a woman who were accused later that year of associating with “a terrorist enterprise” and sabotaging high-speed train lines in France.

In addition to Mr. Halpin’s assertions, documents connected to the case indicate that prosecutors in Paris looked to American officials to provide evidence about a handful of people in the United States and events that took place in New York in 2008.

“Mark Kennedy spied upon myself on United States soil, as well as Julien Coupat and Yildune Levy,” Mr. Halpin wrote in an e-mail, naming two defendants in the group known in France as the Tarnac 10, after the small mountain village where several of them had lived in a commune.

Mr. Halpin added that Mr. Coupat introduced him to Mr. Kennedy in the fall of 2007. “It appears that Mark Kennedy also passed information to the F.B.I. that I knew Julian Coupat,” he added.

Reached via e-mail on Thursday, Mr. Kennedy, who now works with The Densus Group, a security consulting firm based in the United States, declined to comment on Mr. Halpin’s statements.

In 2010, Mr. Halpin said that F.B.I. agents detained him for five hours after he arrived at John F. Kennedy International Airport from Europe, seizing his computer and threatening put him in jail if he did not agree to provide information about Mr. Coupat. Mr. Halpin said that he refused but the agents let him go when they were asked to explain the charges against him.

A spokesman for the F.B.I. in New York, James Margolin, declined to comment on the encounter described by Mr. Halpin.

The accounts of events in New York provided by Mr. Halpin and others added a new twist to two dramas that have received widespread attention in Europe, where they have slowly unraveled over the past few years.

Mr. Kennedy’s actions while spying on political activists in Britain have brought embarrassment to Scotland Yard, as officials there have been forced to confront allegations of inappropriate behavior by some undercover operatives.

As reported in The Guardian newspaper, Mr. Kennedy was said to have had sexual relationships with a number of women connected to groups he had infiltrated.

In 2011, the trial of six people accused of planning to take over a coal-fired power plant collapsed amid claims, denied by Mr. Kennedy, that he had acted as an agent provocateur. Mr. Kennedy was also shown to have worked undercover in more than 20 other countries, including Iceland, Spain and Germany, where members of parliament have raised questions about his role.

Eventually, 10 women, including three who said they had intimate relationships with Mr. Kennedy, sued the police in London saying that they had formed strong personal ties with undercover officers. Later, it was reported in British papers that Mr. Kennedy sued the police, saying that his superiors had failed to prevent him from sleeping with an activist and falling in love.

In France, l’affaire de Tarnac, as it is known, has become a cause célèbre among civil libertarians who have criticized the use of terrorism statutes against people suspected of sabotage but not accused of harming anyone. The defendants have denied wrongdoing, but the authorities have portrayed them as dangerous subversives who plotted attacks against the state then “refused to answer questions, or gave whimsical answers” about their activities.

An unusual element of the case involves a book called “The Coming Insurrection” by an anonymous group of authors called the Invisible Committee. The book advocates rebellion against capitalist culture, encourages readers to form self-sufficient communes and calls for “a diffuse, efficient guerrilla war to give us back our ungovernableness.” Prosecutors have said that Mr. Coupat and his comrades wrote the volume. The suspects denied authorship but Mr. Coupat told journalists in France that the book had merit.

While the Tarnac case has moved slowly through the French legal system, documents have emerged showing that F.B.I. agents were posted outside the Manhattan building where the activists gathered in 2008, videotaping the arrival and departure of Mr. Halpin, Mr. Coupat and Ms. Levy, among others. Those tapes were later given to French prosecutors along with a detailed log compiled by the F.B.I. agents.

As the French investigation continued, documents show that prosecutors in Paris asked officials in the United States about a “meeting of anarchists” in New York and about several people who could be connected to Mr. Coupat. They also asked for information about a low-grade explosive attack in March 2008 that damaged an armed forces recruitment center in Times Square.

In 2012, letters show that Justice Department officials said they had not identified any connection between the people at the Manhattan gathering and the attack on the recruitment center. The officials also gave French prosecutors background information on some American citizens who appeared to have visited the commune in Tarnac and records of an interview that F.B.I. agents had conducted with an assistant professor and French philosophist at New York University who had translated “The Coming Insurrection.”

The professor, Alexander Galloway, told the agents that he had taught the books in a class on political theory and French philosophy, but had never met Mr. Coupat.

Official documents do not mention Mr. Kennedy but several people from New York said that he spent about a week there in early 2008 on his way to visit a brother in Cleveland. During that period, witnesses said Mr. Kennedy attended several informal gatherings, sometimes with Mr. Coupat and Ms. Levy.

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March 15, 2013, 3:06 pm
By COLIN MOYNIHAN

Find this story at 15 March 2013

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