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Marc Lamparello’s story seemed off from the start.

It was nearly 8 p.m. on Wednesday when Mr. Lamparello, a 37-year-old graduate student and lecturer on philosophy, entered St. Patrick’s Cathedral in Midtown Manhattan toting two gasoline cans, lighter fluid and lighters, the police said.

Hours before, he had purchased a $2,800, one-way plane ticket to Rome, which was set to depart the next day.

Mr. Lamparello was about 20 feet into the church when ushers approached him and said he could not be inside the building with the cans of gasoline, the police said. He explained that he was trying to take a shortcut through the iconic sanctuary to reach his van, which he claimed had run out of gas.