As in his parents and sister.

Nope, I was on that tangent also. I was getting the impression that (and I may be slightly morbid and twisted here, but hey...) that the trinity killer is reenacting the death of his family - his sister, then his mother, then finally his father. I was thinking that his father did something terrible to his sister, something along the lines of sexual abuse and this led to either a) her killing herself in the bathtub or b) her father killing her in the bathtub. After his mother found out, she killed herself. Overcome by rage at his father for destroying his family, the trinity killer bashed his father's head in with a hammer. He keeps repeating this pattern over and over again for whatever reason - remorse, anger or a need for closure.

So, what do you think?

I think he killed his father for beating him, that scene when he provoked that guy outside of the bar into fighting back and then all that weird stuff he said... It just really struck me as him acting out some prior incident.

It hadn't crossed my mind about the dad abusing the daughter, that's an interesting theory, it definitely makes sense. I'm just not sure if she was homicide or suicide, the thing with the mirror is throwing me.

I totally think you're spot on about the mom killing herself. She's the only one I', completely positive was a suicide.

Oh yeah, I forgot about him provoking that fight outside the bar... Maybe his dad was just generally abusive, good call! And I have to agree, the mirror thing is pretty weird, I couldn't figure out that either!