So my hero is a serial-killer.

You want your protagonist to be sympathetic, you know. No matter how charming, a serial killer is still a serial killer.

I had decided to change that to a jewelry thief, and started the changeover, and it was doable.

But it seemed to take all the energy out of the book.

Grandy is irredeemable as a human, but he is still a hero, if a hero sacrifices himself for the greater good.

All very weird and likely to put off some people. But then again, the people who would be put off by it aren't going to buy a book whose tagline is "When the Devil is your client...you're in trouble."

So onward with the original conception.