A few hours after the town hall meeting began, deep into the question-and-answer portion, Bill Finnegan lined up for a turn at the microphone. He had not come with any intention to speak, but as the evening dragged on, he changed his mind.

A Muslim group had made a deal to buy an empty convent from the Catholic parish of St. Margaret Mary in the Midland Beach section of Staten Island and open a mosque. A civic association organized a meeting with representatives of the group, the Muslim American Society, on the evening of June 9. Mr. Finnegan had gone, he said later, to “see what all the hoopla was about.”

There were many statements from the audience dressed up as questions to the Muslim representatives: Were any parts of the Koran incorrect? Would they denounce Hamas and Hezbollah, and wasn’t it true that they were connected to those groups? Didn’t all terrorists come out of mosques?

Mr. Finnegan, 25, began by introducing himself. “I said, ‘My name is Bill Finnegan, and I’m a United States Marine recently returned from Afghanistan,’ ” he said.