TinaP, it's a good start.

I don't gather you're setting out to be an encyclopedia of murder ballads (or are you?) but here are a few murder ballads I'm familiar with which you didn't mention. Some of these may not technically be ballads, but they're (mostly) good songs with murders in them.

Lord Randall (The most obvious one, to me.)
Frankie & Johnny
Pearl Bryan
Banks of the Ohio
Eggs & Marrowbone
Binnorie
Dowie Dens of Yarrow
The Bonnie Earl of Moray
Duncan and Brady
Billy DeLyons and Stagolee
Young Hunting
Lady Dysmal and the Kitchen Boy
Charles Guiteau
The Outlandish Knight
The Lonesome Willow Tree
Mary Hamilton
Omie Wise
Poor Ellen Smith

and on and on and on, of course.

Dave Oesterreich