The coordinating efforts by such groups as NCADP, Equal Justice USA, and their financial backers, have helped grow this new demographic by opening up dialogue between groups who have historically opposed the death penalty and others such that may share a common interest, such as pro-life groups, evangelicals and libertarians. Gallup's questions indicate that this group of "morally support but in practice favor life" consists of approximately 1 in 6 Americans. This numbers has been growing every year. Perhaps the Gallup poll's findings could be best summed up in the words of the Cato Institute's founder, Edward H. Crane, "[m]y own view on capital punishment is that it is morally justified, but that the government is often so inept and corrupt that innocent people might die as a result. Thus, I personally oppose capital punishment."
The results of this outreach are being felt beyond polls like Gallup. Death row today is almost 10% lower than it was at the turn of the millennia due chiefly to a lower number of new death sentences. While part of that reduction may be due to other factors, the decline in death sentences seemingly buttress Gallup's findings, a third way on the death penalty, those who are not opposed morally to the death penalty but think that there is a better way than governments killing what they deem to be its worst miscreants.
DPIC, the Travelling Jesuit over at the TCASK & my own blog have more.