I think the pain and torture of botching the murder is the point.

It really isn't. Just like the death penalty itself, how it is done is not a deterrent at all. No one committing murder takes that into consideration.

That said, Tennessee really botched this badly. It was a perfect storm of likely expired drugs, and a woman with incredibly damaged veins that just couldn't handle an IV. Even expert phlebotomists could fail to start a functioning IV in a case like this. And there's the added problem of finding an expert who is ok with being involved in ending someone's life.

I used to think that death by inert gas inhalation - like nitrogen or helium - would be a painless execution method, but new information shows it might still cause suffering.

I'm not sure what the best humane execution method is: firing squad, guillotine, hanging are all brutal and not guaranteed to be pain free. I guess you could wrap someone's head in TNT and disintegrate their brain in a microsecond, but the family of the convict might object to a corpse with no head.

nbcnews.com - Was mess tennessee fails execute inmate lethal injections