It has always struck me as odd that, in the usual last verse, the final couplet usually does not rhyme:

I killed the only girl I loved
Because she would not be my bride

or

I killed the girl that I loved best
Because she would not be my bride.

It does not seem like a major leap to change it to something like:

"I killed the one I love," I cried
"Because she would not be my bride."

and yet I have not seen this kind of change in any of the lyric versions I have found.

I have also found a new final stanza where Willie gets his comeuppance:

The very next day at half past four
The sheriff walked up to my door
He said, "Young man, don't you try to run.
You'll pay for the awful crime you've done."