The last verse Derek is missing is for instance in Martin Carthy's version on his second album (songtitle: Two butchers):

Oh the day it being the market day there were people passing by
Who saw the awful murder who saw poor Johnson die

(copied from Garry Gillard's MC&Watersons site)

Not the same as Sweeney's Men are singing but the gist of the story is there. I'll try to hear what SM are singing in the last verse tonight.

Wolfgang