W. M. Daniels recalls that Joseph probably tried to escape to save the others in the room.
Charles Wesley Wandell, History of the persecutions!! endured by the Church of Jesus Christ of Latter-day Saints, in America compiled from public documents, and drawn from authentic sources. By C.W. Wandell, minister of the gospel (Sydney: 1852), 55
Elder Richards was contending with the assailants, at the door, when Joseph, seeing there was no safety in the room, and probably thinking it might save the lives of the others if he could escape from the room, turned calmly from the door, dropped his pistol upon the floor, saying, "There, defend yourselves as well as you can."
W. M. Daniels was not a member of the Church when he was in the militia at Carthage, but he appears to have joined later.