It's time to abolish it until further reforms can be completed.
If you cannot absolutely prove a person's guilt 100%, then the punishment likewise cannot be absolute. Far too many innocent people have been exonerated, many of whom would have been murdered by the state.
Whether it deters crime is such a completely irrelevant and variable question that no conclusion will ever be reached.
I say execute when there is no doubt and when it can be done quickly. Until then, let the penalty be abolished.