I'd go along with that, except that I think it's on a more subtle level. He is fantasizing about quitting and getting the cash to live happily ever after, but he's not going to pull that off, and it will only make him angrier.
The hope is that he'll give enough clues in this ill-fated ransom attempt that he'll be caught now.
When he determines that he can't get the money, and get out of the killing cycle, he's going to be a very angry person, and he'll express that through another multiple killing day to punish us all.
You might be right on. Of course, angrier may make him more careless too. I hope he slips up soon.