It IS possible to execute a human being painlessly and without unnecessary trauma.
Sodium pentobarbital, the same drug commonly used to euthanize animals, will humanely bring down a 1000 pound horse in seconds when correctly administered by qualified personnel. The horse merely goes to sleep and death follows rapidly. The horse is totally unaware of the transition from sleep to death.
The point here is that the same procedure, using the same drugs can be used on human animals. The key is that the procedure MUST be done by individuals trained in the proper use of the drugs and equipment necessary to accomplish the task.
One solution might be to have an 'official' executioner. A person specifically trained to perform this service. Such an individual would have a genuine interest in doing his/her job at the highest level of competence. Such a position would relieve the staff eg. wardens, guards etc. of the responsibility of performing a medical procedure without proper training.

Isn't the greatest pain though, in the case of human beings, the knowledge of the forthcoming death?

Absolutely! That is the one part that we can't fix, and I'm not really sure that we should even try!
My comment was aimed solely at the ABSOLUTELY UNNECESSARY physical suffering that we put a lot of condemned inmates through.
The solution is not to abolish capital punishment but to do it RIGHT!
We have the means at our disposal and have had for years.

Absolutely! That is the one part that we can't fix

Can't we really?

@Fast T friend:
Do you have a suggestion?

I don't have a solution, I have a stance though and it is simple: let us stop killing people.

OK! Then where do we put the folks that want to kill US?

There is a long stretch of options, most of which involve incarceration. Hopefully at some point we'll understand more than we do now and maybe be able to alter certain states that result in violence with other means.
I don't like the concept of depriving someone of freedom in its most basic form as prisons do, but i accept it as means of regulation in a human society. Killing however falls out of the category of means to sustain human society in my book.

Unfortunately, we are rapidly running out of room to hold incarcerated individuals. Also, you and I and everyone else who works for a living indirectly pays for the prisoner's expenses.
And I ask you, if you had a pet dog that became vicious and a threat to your neighbors, would you lock it in a cage for the rest of it's life or would you consider having it euthanized?

I doubt that we'll reach an agreement on this issue. However, I will add just this: I see the payment you refer to as a payment to uphold a certain oder in the society I live in. So, yes, I am prepared to make that payment. It makes greater sense to me than taking someone's life.
That said, I don't expect to change your view cpltaiji , I hope though we both gained something out of this exchange

What we are willing to pay for is a big indicator of our values. And what we are not willing to pay for.

Yep, I agree.

@Fast T friend:
I believe we did. I'm just curious why you chose not to respond to my question.

"And I ask you, if you had a pet dog that became vicious and a threat to your neighbors, would you lock it in a cage for the rest of it's life or would you consider having it euthanized?"

I don't take the same measures with dogs and men. call me prejudiced

Interesting!

I can live with 'interesting'