Lethal Injection: Inhumane?

The Sumpreme Court is scheduled to hear a case on whether lethal injection is humane. Opponents of lethal injection claim that if it is not done perfectly, it can cause excrutiating pain. Someone please explain to me why this is a concern. So what these people are saying is that people like Timothy McVay deserve a peaceful, painless release from the horrible crimes that they comitted? In my opinion, lethal injection is too mild in the first place. Inmates on death row are people that kill people. Is there anyone out there who thinks that a little bit of pain from an injection comes anywhere close to making up for the pain that they caused their victims and their families? There is a reason that people are put on death row: they don't deserve to be here anymore. I'm not saying that America should go back to be-heading or hanging but seriously, give me a break. A little prick in the arm and that's all? And now we want to make it even milder? What happened to suffering the consequences of one's actions? The only comfort that I can take from this is that hopefully they will get what they deserve in the long run.