Still in most Prisons. Let's the condemned have just a few seconds to realize....THIS is what you get when you are a monster in today's society. August 6th, 1890, America's invention "the chair" was used to execute wife murderer, William Kemmeler.

Well crafted oak chair..
OR,.... another oldie but a goody for scumbags

Cyanide pellet into a simple tub of chlorine, basic chemistry. 100% effective.
We are a nation of laws that have consequences. The more serious and horrendous the crime, the consequences should match the lethal nature of the convicted.
Although, Public hangings for drive by gangsters that kill innocent bystanders and children in the crossfire, in THEIR neighborhood would maybe send a message. Firing squads always get the thumbs up for capital crimes.
But we're a "kinder, gentler" nation.