Thanksbrokenbackjack!!
I see that your examination if this subject is revealing greatly so,
great with the text of Annie's and/or the movie.
It does increase this as a puzzle further for me.
May I take two of your sentences:
Ennis obviously suspected that dear old dad was among the killers. Yet even he didn't know.
...
It could be that Ennis's father was trying to be protective... and sought to be somewhat manly in his way
to protect his two sons. I will come back to that later, if you want... remind me.
However, it could be like Ennis thinks that his dad was the or one of the killers... as he mentions that (this idea) to Jack!! Hard to hear, hard to say... why would Ennis say that of his father??
WHY INDEED!!
Ennis did maybe think his dad was a killer? Or thought that his dad was probably so: a killer?
I know of a gay friend who told me that his first father was a criminal... and I will recheck with him to see if he says his dad was a killer. His first dad is deceased!
So maybe Ennis's father was a criminal, in more that one way?? All his life?? Even was a murderer?? Hard statement... hard for Ennis to think that??
I heard of a neighbour who placed a bomb at the police station!! Wow, wow!! Criminals...murderers, hate gay men... it seems to me. Some persons prefer to be criminals, even murderers. There seems to be evidence in Annie's book or in the movie that Ennis' father was much more than just a dad, like a criminal even. There are more than one clues!! ??
That is disconforting... was Ennis's father such a bad apple?? And he sought that his boys were to become criminals too??
Does Annie mention that Ennis's father showed that horrible scene of the murdered gay man (of the couple), to his two boys or only to Jack??
You saw that Ennis did not know if his dad was the or one of the killers... but it could be that he did know??
There is also other disturbing evidence in the movie.
Awaiting your thoughts, research, ideas, etc.,
hugs!!