Early Ossipee postmark, but the story of this cover is the addressee, Seth W. Fogg.  According to Boston records:

Commonwealth Vs. Timothy Hurley.

Evidence that one of a noisy crowd near a police officer cried "Kill the damned son of a bitch." about the time when others knocked the officer down, is sufficient to warrant his conviction for an assault upon the officer.

Indictment for an assault upon Seth W. Fogg, a police officer, on July 4,1867, at Boston. On the trial in the superior court, before Brigham, J., Fogg testified that, about five o'clock in the afternoon of the day charged, he was in Kneeland Street in Boston endeavoring to take a prisoner to the police station, when a crowd of at least two hundred persons gathered there, some of whom knocked him down, but " that he did not receive a blow to his knowledge from the defendant, nor hear his voice, nor see him on said day until he saw him in the station-house after his arrest." Joseph M. Towne, another police officer, testified that the crowd was of "not far from five thousand people," and that he saw the defendant not further than four or five feet distant from Fogg, and heard him cry out there, "Kill the damned son of a bitch!".