I can understand being frustrated that someone "gets away" with a crime or spends the rest of their life in prison rather than being put to death. Rather than railing against the defense attorney perhaps the concerns should be with the course of the police investigation. If a defense attorney is able to find flaw in the investigation, then this creates reasonable doubt. Remember that our justice system is created to only find guilt when there is a preponderance of guilt and no reasonable doubt.
These murderers aren't exactly walking free. They are spared the death penalty because often evidence is called into question due to inconsistencies or the lack of appropriate pursuit by law enforcement. With this in mind, the prosecution's case will fail to meet the requirements for a sentence of death.
More information about formatting options