If he was as confident as his PA public defender attorney made him out to be, keeping in mind he had no clue what was in the PCA...you have to wonder if there's some disassociation going on with the guy. Seems like he had a completely different understanding of that night.
People have been pointing to the purported 'Better shopping in Moscow' quote attributed to him (paraphrasing) as some sort of sick joke on Bryan's part. But IMO, I interpreted it as signs of the preparation he's been doing in case he's ever questioned about his white Elantra. Believing that the only thing he'd have to explain is the amount of times his car has been caught in Moscow.
So you have to wonder if he thought in his head he pulled off the perfect crime.
I'm standing by my theory that, as successful as he was academically, maybe he wasn't in a place personally
that he wanted to be at this stage of his life. No wife, no girlfriend, no significant other on the horizon. No job prospects. Close to graduating with a degree that might actually be useless unless he wanted to go into university level teaching (which I don't think he did).
We know from his past that he had LE (and Army Rangers) aspirations, but it appears the closest he ever got to that was a short stint as a security officer at a school. What was his next step in life? Did he really want a career? Who would hire him with nothing but book knowledge and next to no job experience in his preferred field?
I honestly think he did have an "eff it" moment like you said. He committed this crime, likely hoping to get away with it, but maybe not really caring if he did get caught. He could spend his time in prison writing his memoirs, maybe even get his former professor to coauthor a book with him. Perhaps he was in love with the idea of hundreds of thousands of people being fascinated with this crime, and, subsequently intrigued by what kind of person could commit such a horrible act.