According to American Jewry and the Civil War by Bertram Wallace Korn, American Jews responded by draping their shuls in black and by substituting Yom Kippur "hymns and chants" for "Passover melodies" (excerpt below) Its not clear if this memorial was performed on the night of the assassination, which was Shabbos Chol Hamoed, or the next week for the 7th and 8th day of the holiday. Its not clear if this was done everywhere, or in a few shuls only. It also seems strange to me that the murder of a president would be observed with Yom Kippur style services, when Tisha B'av, not Yom Kippur, is the holiday associated with mourning.
Does anyone know more?
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