An O'Brien descendent told me that Jimmy and Mick used to be friends, but fell out one day while fishing at a local creek.
After Mick had thrown a fishing net over the water, he wanted Jimmy to swim to the other side to fasten it.
A punch up resulted when Jimmy refused.
Then Mick's older and much bigger brother, Ted, appeared on the scene and got seriously stuck into Jimmy.
Mick was egging him on, shouting: 'Kill the black bastard!'
Ted only revealed this story on his death bed, suggesting he felt guilt about the role he played in the murder of his sister-in-law.
A shadow puppet play about this incident, and Jimmy's subsequent return to the O'Brien home with a tomahawk to commit murder, can be seen at http://vimeo.com/31173858.
Only a snippet of this appeared to me to have been used in the play for which it was created, Posts in the Paddock, staged in Sydney last November.
There is also a short video of parts of the play at http://vimeo.com/36010647.