Muck was arrested on March 25, 1918, just before midnight and therefore the BSO's performances of Bach's "Saint Matthew Passion" on March 26 and April 2, which Muck had been preparing for months, had to be conducted by Ernst Schmidt. Government officials were free to ignore the fact that he was a Swiss citizen and bearer of a Swiss passport, since the law sanctioned the arrest of those born anywhere in Germany before the founding of the German Empire without respect to citizenship. Boston police and federal agents also searched Muck's home at 50 Fenway and removed personal papers and scores. They suspected the conductor's markings in the score of the "St. Matthew Passion" were code indicative of pro-German activity. He was imprisoned at Fort Oglethorpe in Georgia until on August 21, 1919, an agent of the Department of Justice put him and his wife on a ship to Copenhagen. The Phi Mu Alpha Sinfonia music fraternity that had elected him to national honorary membership in 1916 expelled Muck in 1919 for sympathizing with the Central powers.