Usually you'll only get put to death if you commits what they call CAPITOL MURDER, which from my understanding is pretty much when you either.... totally overkill... or torture, or I when you PLAN to do it rather than it being some random thing... I believe in most cases while being charged with capitol murder you can plead guilty for a reduced charge.
In the end, the laws/punishments, especially in the US are greatly unbalanced and dumb for example:
If you sell drugs to a child and they die because of it, you get like 5 years in prison, or more likely you get a new identity and living paid for by taxpayer if you turn on your supplier.
If you're 17 yrs old, and you send a picture of your dick to you 17 yr old girlfriend, or you look at a similar picture or even one of a 17yr old in like.. underwear.... you get marked as a sex offender the rest of your life... FOREVER, you can't get a job, state/gov assistance, and can't rent a place to live, most likely you wouldn't be able to get a loan for a home mortgage either or for a car.