Slow Execution...or Just Punishment?

Death penalty opponents are up in arms about the recent execution of Dennis McGuire who was convicted of kidnapping, raping, and murdering 22 year old, pregnant woman, Joy Stewart.  He was executed using a new combination of lethal drugs.  However, those drugs were untested and caused what is known as "air hunger". Where the dying person struggles to breathe and is in pain and fear during their last moments. Kind of like Joy Stewart must have been, correct?