Everyone here is assuming that the plot summary and the protagonist correctly identify the ultimate culprit for the murder, but despite people's high expectations for the tension from that I'm just sitting here going, "nothing's even shown she did it, this could still be a complete nothingburger..."
You'd think someone with overwhelming magical power, fame, connections, and can easily make a fortune in a single night could come up with a way to make his disabled wife's life a little more comfortable rather than just becoming a recluse. Ancient rejuvenation magic exists but he can't do anything to help with a spinal injury? Not even a helper golem.
It still mostly pulls it off on Vibes, but adding magic to the mix definitely accentuates the classic "I see your hyper-competence extends to all areas except 'doing anything that might have hampered the development of your tragic backstory' " problem.
We are seemingly asked to simultaneously believe that he does everything for his family, that he is extremely powerful and competent, and that this was him doing his best. Unless some drastic new information is revealed that reframes everything is revealed hereafter, one of those three things must surely be false?
Now, the most plausible explanation of course would be that he's been terminally depressed and
wasn't really trying his best at all, dragging his feet through life after his daughter's death and essentially neglecting the care of his spouse in the process. There would I suppose be in that case some nice and dramatic irony in him only being only finally motivated at last by rage, and never by the love and care we're so earnestly told drove him.
I'm not sure the author's realized that, though, because if they had (with how this has gone so far) I feel like MC would have done a full-throated lament about his own tragic flaws already. Subtlety does not seem to be this story's thing.