I love this discussion - I have recently chosen two new songs to learn. but they are not ready for public consumption yet - I want to get them just right, because they are both "murder songs", if you define that as a song in which one of the particulars is wrongfully killed. They both come off a CD called English & Scottish Folk Ballads, they're sung by a variety of musicians. A.L. Lloyd is the first singer listed, produced by Topic Records in London, c1996.
The first song is The Bramble Briar, in which a servant and the daughter of the household fall in love, and her brothers kill him. The second is Jack Orion, who kills his apprentice for cuckholding him with a lady that invited Jack to her chamber. I wonder if that one was originally considered a wrongful killing, b/c the apprentice had sex with a Countess, and that was probably punishable by death back then. Anyone know? By today's standards, it is a murder, though, so I'm treating it as one. I've had fun working with the melodies and set up, trying to get them to a point that today's audience, with much shortened attention span, will find enough interest (varied melodies, chorus, etc.). I am a bit concerned about performing them, don't know how the people will react, but I'm willing to try it.
As to why they're so fascinating, I would direct your attention to similarities with True Crime Novels, as another place to look for reasons, for people to ask why they like them.
There has always been a place for the ballads, and they are perhaps being replaced by the TC novels. People are always interested in what their fellows have done wrong, or misfortunes that have befallen them, whether it's the "there, but by grace go I", curiosity, morbidity, or some other reason. That would be the interesting discovery of you research. There's also some similarity with the talk shows that go on, sensationalism, and tabloids.
I, for one, would be interested in reading your findings!
Have fun with it,
Pioden