“Bullet-Brain”
I typically prefer quick painless executions. But this case is certainly an exception.
A bullet being fired into the perp’s brain is too good.
Maybe taking a bullet’s projectile, and slowly driving it into his head with a hammer and punch would be OK. Personally, I’d try several non-fatal locations, one at a time, with a week or so break in between. Sooner or later, (hopefully much later), he will be roasting in Hell.
Vincent Prices “Pit & Pendulum”, first cut to his toes, then slowly, ever so slowly, cut the way up.’