I honestly don't find capital punishment to be wrong in principle. I just doubt its effectiveness as a deterrent. Its implementation is flawed to the point that it seems like a bad idea. It's more expensive to execute a prisoner than to keep him in prison for the rest of his life due to all the legal fees involved in death row.
Today, I read this account of how Cameron Todd Willingham was sentenced to death and executed based on questionable circumstantial evidence, inconsistent testimony of other people, and other such uncertainties. He might have been spared, but the review board was arbitrarily unwilling to consider new evidence, etc.
Executing an innocent person is absolutely intolerable. The review board members should be put on trial for manslaughter. This case should be thoroughly investigated and capital punishment should be suspended at least until the system has been properly audited.