On Jan. 7, the police cordoned off the streets. The auditorium’s ventilation and elevators were turned off. Every light bulb in the concert hall was unscrewed to eliminate a faint buzzing sound.

Upstairs in the museum, Mr. Cacciatori put on a pair of velvet gloves and took a 1615 Amati viola from its glass display case. He inspected it thoroughly, and then a security guard escorted him and the instrument down two flight of stairs to the auditorium.

The curator handed the instrument to Wim Janssen, a Dutch viola player, who walked to the center of the stage.

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