It would have been 1000% more believable that he, as a retired detective, would realize that there was no chance of this uber-rich guy being held responsible, and shooting him. Then claiming "extreme emotional disturbance" and hoping the jury would pretty much hate the pedo so much that they nullify. I mean, I think I've heard of that before. Like on a Law & Order episode.
I did start to wonder though, is Detective Nick really a stand-up guy? They made the mom such a mess, and we are supposed to believe he is a good guy cuz he's a cop and not in rehab? Maybe those 2 girls have been living in a super dysfunctional home since forever? And this turn of events is related to that? Would explain Ivy's willingness to throw her little sis into the mix.