Thanks for sharing something so personal. I find the rationale in the article perplexing. Anyone would be laughed out of court if their defense for driving drunk was that they were a safe and able drunk driver. Even if that was 100% true and they were able to drive an obstacle course drunk they should and would still be charged. DUI means driving under the influence, it doesn't mean driving poorly under the influence. Add to all of that a death then there is no way it should not be considered manslaughter while driving under the influence.
This kind of thing saddens and worries me. I spend a lot of time on the roads running and cycling and you always do all you can to make sure you are seen and out of harms way. Someone driving under the influence of anything, especially something that is illegal to have in the first place, is not going to be as able to avoid anyone as the same driver would sober.
I'm sorry that the tragic death of your father has to be compounded by the tragic stupidity of the prosecution.